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	$90.73	8.136%	$98.1118	$98.11	$98.10	$98.10
Purchase #2	$34.34	4.260%	$35.8029	$35.80	$35.80	$35.80
Purchase #3	$246.95	5.519%	$260.5792	$260.58	$260.60	$260.60
Purchase #4	$55.29	11.544%	$61.6727	$61.67	$61.65	$61.70
Purchase #5	$156.50	5.732%	$165.4706	$165.47	$165.45	$165.50
Purchase #6	$83.56	8.490%	$90.6542	$90.65	$90.65	$90.70
Purchase #7	$93.57	10.211%	$103.1244	$103.12	$103.10	$103.10
7 purchase totals =	$760.94		$815.4158	$815.40	$815.35	$815.50