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	$233.67	8.548%	$253.6441	$253.64	$253.65	$253.60
Purchase #2	$167.65	12.129%	$187.9843	$187.98	$188.00	$188.00
Purchase #3	$64.44	12.733%	$72.6451	$72.65	$72.65	$72.60
Purchase #4	$101.32	13.740%	$115.2414	$115.24	$115.25	$115.20
Purchase #5	$61.73	6.330%	$65.6375	$65.64	$65.65	$65.60
Purchase #6	$60.51	9.762%	$66.417	$66.42	$66.40	$66.40
Purchase #7	$73.71	6.142%	$78.2373	$78.24	$78.25	$78.20
7 purchase totals =	$763.03		$839.8067	$839.81	$839.85	$839.60