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	$16.43	11.562%	$18.3296	$18.33	$18.35	$18.30
Purchase #2	$92.54	9.567%	$101.3933	$101.39	$101.40	$101.40
Purchase #3	$133.81	9.592%	$146.6451	$146.65	$146.65	$146.60
Purchase #4	$176.61	12.450%	$198.5979	$198.60	$198.60	$198.60
Purchase #5	$196.66	8.569%	$213.5118	$213.51	$213.50	$213.50
Purchase #6	$98.60	12.643%	$111.066	$111.07	$111.05	$111.10
Purchase #7	$141.69	5.426%	$149.3781	$149.38	$149.40	$149.40
7 purchase totals =	$856.34		$938.9218	$938.93	$938.95	$938.90