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	$45.27	3.132%	$46.6879	$46.69	$46.70	$46.70
Purchase #2	$141.47	13.642%	$160.7693	$160.77	$160.75	$160.80
Purchase #3	$229.90	4.432%	$240.0892	$240.09	$240.10	$240.10
Purchase #4	$174.96	9.103%	$190.8866	$190.89	$190.90	$190.90
Purchase #5	$232.64	11.298%	$258.9237	$258.92	$258.90	$258.90
Purchase #6	$65.72	8.275%	$71.1583	$71.16	$71.15	$71.20
Purchase #7	$67.70	5.848%	$71.6591	$71.66	$71.65	$71.70
7 purchase totals =	$957.66		$1,040.1741	$1,040.18	$1,040.15	$1,040.30