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	$199.30	12.428%	$224.069	$224.07	$224.05	$224.10
Purchase #2	$129.74	9.104%	$141.5515	$141.55	$141.55	$141.60
Purchase #3	$79.45	7.791%	$85.6399	$85.64	$85.65	$85.60
Purchase #4	$149.77	10.103%	$164.9013	$164.90	$164.90	$164.90
Purchase #5	$127.61	7.821%	$137.5904	$137.59	$137.60	$137.60
Purchase #6	$52.62	9.155%	$57.4374	$57.44	$57.45	$57.40
Purchase #7	$120.48	5.797%	$127.4642	$127.46	$127.45	$127.50
7 purchase totals =	$858.97		$938.6537	$938.65	$938.65	$938.70