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	$49.48	5.218%	$52.0619	$52.06	$52.05	$52.10
Purchase #2	$66.32	8.312%	$71.8325	$71.83	$71.85	$71.80
Purchase #3	$133.53	11.425%	$148.7858	$148.79	$148.80	$148.80
Purchase #4	$137.50	4.700%	$143.9625	$143.96	$143.95	$144.00
Purchase #5	$15.33	10.390%	$16.9228	$16.92	$16.90	$16.90
Purchase #6	$33.59	11.229%	$37.3618	$37.36	$37.35	$37.40
Purchase #7	$31.42	10.344%	$34.6701	$34.67	$34.65	$34.70
7 purchase totals =	$467.17		$505.5974	$505.59	$505.55	$505.70