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	$39.98	12.696%	$45.0559	$45.06	$45.05	$45.10
Purchase #2	$229.96	11.575%	$256.5779	$256.58	$256.60	$256.60
Purchase #3	$27.47	11.131%	$30.5277	$30.53	$30.55	$30.50
Purchase #4	$83.39	7.520%	$89.6609	$89.66	$89.65	$89.70
Purchase #5	$137.49	7.436%	$147.7138	$147.71	$147.70	$147.70
Purchase #6	$143.89	10.543%	$159.0603	$159.06	$159.05	$159.10
Purchase #7	$85.63	5.362%	$90.2215	$90.22	$90.20	$90.20
7 purchase totals =	$747.81		$818.8180	$818.82	$818.80	$818.90