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	$132.56	10.361%	$146.2945	$146.29	$146.30	$146.30
Purchase #2	$50.87	7.316%	$54.5916	$54.59	$54.60	$54.60
Purchase #3	$192.50	9.354%	$210.5065	$210.51	$210.50	$210.50
Purchase #4	$146.89	6.831%	$156.9241	$156.92	$156.90	$156.90
Purchase #5	$35.51	13.447%	$40.285	$40.29	$40.30	$40.30
Purchase #6	$176.35	10.552%	$194.9585	$194.96	$194.95	$195.00
Purchase #7	$121.25	5.723%	$128.1891	$128.19	$128.20	$128.20
7 purchase totals =	$855.93		$931.7493	$931.75	$931.75	$931.80