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	$74.43	12.161%	$83.4814	$83.48	$83.50	$83.50
Purchase #2	$173.89	8.488%	$188.6498	$188.65	$188.65	$188.60
Purchase #3	$11.91	11.548%	$13.2854	$13.29	$13.30	$13.30
Purchase #4	$149.71	13.357%	$169.7068	$169.71	$169.70	$169.70
Purchase #5	$131.94	7.321%	$141.5993	$141.60	$141.60	$141.60
Purchase #6	$61.87	11.240%	$68.8242	$68.82	$68.80	$68.80
Purchase #7	$32.31	9.523%	$35.3869	$35.39	$35.40	$35.40
7 purchase totals =	$636.06		$700.9338	$700.94	$700.95	$700.90