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	$120.76	13.548%	$137.1206	$137.12	$137.10	$137.10
Purchase #2	$86.83	4.338%	$90.5967	$90.60	$90.60	$90.60
Purchase #3	$134.74	9.462%	$147.4891	$147.49	$147.50	$147.50
Purchase #4	$126.54	13.263%	$143.323	$143.32	$143.30	$143.30
Purchase #5	$143.69	7.500%	$154.4668	$154.47	$154.45	$154.50
Purchase #6	$94.42	4.663%	$98.8228	$98.82	$98.80	$98.80
Purchase #7	$129.32	13.576%	$146.8765	$146.88	$146.90	$146.90
7 purchase totals =	$836.30		$918.6955	$918.70	$918.65	$918.70