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	$83.91	5.857%	$88.8246	$88.82	$88.80	$88.80
Purchase #2	$182.69	8.507%	$198.2314	$198.23	$198.25	$198.20
Purchase #3	$12.96	4.869%	$13.591	$13.59	$13.60	$13.60
Purchase #4	$247.91	12.855%	$279.7788	$279.78	$279.80	$279.80
Purchase #5	$28.50	9.548%	$31.2212	$31.22	$31.20	$31.20
Purchase #6	$53.29	13.850%	$60.6707	$60.67	$60.65	$60.70
Purchase #7	$98.95	12.216%	$111.0377	$111.04	$111.05	$111.00
7 purchase totals =	$708.21		$783.3554	$783.35	$783.35	$783.30