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	$149.96	6.406%	$159.5664	$159.57	$159.55	$159.60
Purchase #2	$61.56	6.351%	$65.4697	$65.47	$65.45	$65.50
Purchase #3	$78.27	3.625%	$81.1073	$81.11	$81.10	$81.10
Purchase #4	$123.34	12.794%	$139.1201	$139.12	$139.10	$139.10
Purchase #5	$81.82	12.469%	$92.0221	$92.02	$92.00	$92.00
Purchase #6	$170.39	10.823%	$188.8313	$188.83	$188.85	$188.80
Purchase #7	$166.25	7.572%	$178.8385	$178.84	$178.85	$178.80
7 purchase totals =	$831.59		$904.9554	$904.96	$904.90	$904.90