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	$18.57	13.713%	$21.1165	$21.12	$21.10	$21.10
Purchase #2	$75.89	12.283%	$85.2116	$85.21	$85.20	$85.20
Purchase #3	$166.59	4.220%	$173.6201	$173.62	$173.60	$173.60
Purchase #4	$45.29	9.646%	$49.6587	$49.66	$49.65	$49.70
Purchase #5	$163.34	13.829%	$185.9283	$185.93	$185.95	$185.90
Purchase #6	$125.92	3.622%	$130.4808	$130.48	$130.50	$130.50
Purchase #7	$200.89	10.155%	$221.2904	$221.29	$221.30	$221.30
7 purchase totals =	$796.49		$867.3064	$867.31	$867.30	$867.30