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	$26.56	7.352%	$28.5127	$28.51	$28.50	$28.50
Purchase #2	$53.43	7.123%	$57.2358	$57.24	$57.25	$57.20
Purchase #3	$68.25	11.504%	$76.1015	$76.10	$76.10	$76.10
Purchase #4	$39.35	8.165%	$42.5629	$42.56	$42.55	$42.60
Purchase #5	$177.46	7.430%	$190.6453	$190.65	$190.65	$190.60
Purchase #6	$240.94	5.548%	$254.3074	$254.31	$254.30	$254.30
Purchase #7	$226.37	13.211%	$256.2757	$256.28	$256.30	$256.30
7 purchase totals =	$832.36		$905.6413	$905.65	$905.65	$905.60