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	$226.93	12.672%	$255.6866	$255.69	$255.70	$255.70
Purchase #2	$75.50	11.118%	$83.8941	$83.89	$83.90	$83.90
Purchase #3	$18.51	8.666%	$20.1141	$20.11	$20.10	$20.10
Purchase #4	$213.58	4.658%	$223.5286	$223.53	$223.55	$223.50
Purchase #5	$204.76	9.527%	$224.2675	$224.27	$224.25	$224.30
Purchase #6	$9.75	10.283%	$10.7526	$10.75	$10.75	$10.80
Purchase #7	$116.90	11.700%	$130.5773	$130.58	$130.60	$130.60
7 purchase totals =	$865.93		$948.8208	$948.82	$948.85	$948.90