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	$122.71	7.324%	$131.6973	$131.70	$131.70	$131.70
Purchase #2	$188.60	11.816%	$210.885	$210.89	$210.90	$210.90
Purchase #3	$9.57	11.489%	$10.6695	$10.67	$10.65	$10.70
Purchase #4	$53.40	10.694%	$59.1106	$59.11	$59.10	$59.10
Purchase #5	$247.27	5.409%	$260.6448	$260.64	$260.65	$260.60
Purchase #6	$209.30	12.467%	$235.3934	$235.39	$235.40	$235.40
Purchase #7	$219.55	7.449%	$235.9043	$235.90	$235.90	$235.90
7 purchase totals =	$1,050.40		$1,144.3049	$1,144.30	$1,144.30	$1,144.30