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	$33.65	10.639%	$37.23	$37.23	$37.25	$37.20
Purchase #2	$219.50	9.276%	$239.8608	$239.86	$239.85	$239.90
Purchase #3	$21.40	5.373%	$22.5498	$22.55	$22.55	$22.50
Purchase #4	$91.89	6.559%	$97.9171	$97.92	$97.90	$97.90
Purchase #5	$49.81	13.250%	$56.4098	$56.41	$56.40	$56.40
Purchase #6	$145.29	13.831%	$165.3851	$165.39	$165.40	$165.40
Purchase #7	$40.68	7.498%	$43.7302	$43.73	$43.75	$43.70
7 purchase totals =	$602.22		$663.0828	$663.09	$663.10	$663.00