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	$153.79	8.662%	$167.1113	$167.11	$167.10	$167.10
Purchase #2	$212.39	9.142%	$231.8067	$231.81	$231.80	$231.80
Purchase #3	$16.91	11.479%	$18.8511	$18.85	$18.85	$18.90
Purchase #4	$127.82	7.551%	$137.4717	$137.47	$137.45	$137.50
Purchase #5	$28.86	11.754%	$32.2522	$32.25	$32.25	$32.30
Purchase #6	$135.26	11.263%	$150.4943	$150.49	$150.50	$150.50
Purchase #7	$41.74	9.740%	$45.8055	$45.81	$45.80	$45.80
7 purchase totals =	$716.77		$783.7928	$783.79	$783.75	$783.90