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	$172.62	9.452%	$188.936	$188.94	$188.95	$188.90
Purchase #2	$120.61	13.684%	$137.1143	$137.11	$137.10	$137.10
Purchase #3	$178.58	13.707%	$203.058	$203.06	$203.05	$203.10
Purchase #4	$219.42	10.532%	$242.5293	$242.53	$242.55	$242.50
Purchase #5	$127.39	3.530%	$131.8869	$131.89	$131.90	$131.90
Purchase #6	$162.31	10.671%	$179.6301	$179.63	$179.65	$179.60
Purchase #7	$37.29	10.146%	$41.0734	$41.07	$41.05	$41.10
7 purchase totals =	$1,018.22		$1,124.2280	$1,124.23	$1,124.25	$1,124.20