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	$147.43	12.248%	$165.4872	$165.49	$165.50	$165.50
Purchase #2	$55.34	10.648%	$61.2326	$61.23	$61.25	$61.20
Purchase #3	$137.45	6.302%	$146.1121	$146.11	$146.10	$146.10
Purchase #4	$86.39	5.290%	$90.96	$90.96	$90.95	$91.00
Purchase #5	$135.88	3.867%	$141.1345	$141.13	$141.15	$141.10
Purchase #6	$17.62	9.463%	$19.2874	$19.29	$19.30	$19.30
Purchase #7	$162.46	11.690%	$181.4516	$181.45	$181.45	$181.50
7 purchase totals =	$742.57		$805.6654	$805.66	$805.70	$805.70