Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$170.72	3.654%	$176.9581	$176.96	$176.95	$177.00
Purchase #2	$139.94	10.385%	$154.4728	$154.47	$154.45	$154.50
Purchase #3	$247.35	8.684%	$268.8299	$268.83	$268.85	$268.80
Purchase #4	$214.33	5.109%	$225.2801	$225.28	$225.30	$225.30
Purchase #5	$107.44	4.315%	$112.076	$112.08	$112.10	$112.10
Purchase #6	$37.61	11.712%	$42.0149	$42.01	$42.00	$42.00
Purchase #7	$172.39	9.484%	$188.7395	$188.74	$188.75	$188.70
7 purchase totals =	$1,089.78		$1,168.3713	$1,168.37	$1,168.40	$1,168.40