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	$116.45	12.821%	$131.3801	$131.38	$131.40	$131.40
Purchase #2	$98.77	13.829%	$112.4289	$112.43	$112.45	$112.40
Purchase #3	$129.85	5.546%	$137.0515	$137.05	$137.05	$137.10
Purchase #4	$64.47	6.261%	$68.5065	$68.51	$68.50	$68.50
Purchase #5	$41.28	10.399%	$45.5727	$45.57	$45.55	$45.60
Purchase #6	$76.61	8.733%	$83.3004	$83.30	$83.30	$83.30
Purchase #7	$73.66	10.383%	$81.3081	$81.31	$81.30	$81.30
7 purchase totals =	$601.09		$659.5482	$659.55	$659.55	$659.60