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	$228.81	11.355%	$254.7914	$254.79	$254.80	$254.80
Purchase #2	$91.51	8.531%	$99.3167	$99.32	$99.30	$99.30
Purchase #3	$136.69	10.553%	$151.1149	$151.11	$151.10	$151.10
Purchase #4	$78.25	9.628%	$85.7839	$85.78	$85.80	$85.80
Purchase #5	$130.30	8.147%	$140.9155	$140.92	$140.90	$140.90
Purchase #6	$28.65	5.265%	$30.1584	$30.16	$30.15	$30.20
Purchase #7	$136.36	6.401%	$145.0884	$145.09	$145.10	$145.10
7 purchase totals =	$830.57		$907.1692	$907.17	$907.15	$907.20