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	$170.40	12.152%	$191.107	$191.11	$191.10	$191.10
Purchase #2	$89.88	3.156%	$92.7166	$92.72	$92.70	$92.70
Purchase #3	$182.86	7.201%	$196.0277	$196.03	$196.05	$196.00
Purchase #4	$240.30	10.546%	$265.642	$265.64	$265.65	$265.60
Purchase #5	$120.94	13.847%	$137.6866	$137.69	$137.70	$137.70
Purchase #6	$73.84	12.733%	$83.242	$83.24	$83.25	$83.20
Purchase #7	$33.51	9.370%	$36.6499	$36.65	$36.65	$36.60
7 purchase totals =	$911.73		$1,003.0718	$1,003.08	$1,003.10	$1,002.90