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	$232.72	4.224%	$242.5501	$242.55	$242.55	$242.60
Purchase #2	$111.82	12.869%	$126.2101	$126.21	$126.20	$126.20
Purchase #3	$155.77	12.648%	$175.4718	$175.47	$175.45	$175.50
Purchase #4	$26.37	9.719%	$28.9329	$28.93	$28.95	$28.90
Purchase #5	$145.88	3.576%	$151.0967	$151.10	$151.10	$151.10
Purchase #6	$187.71	13.552%	$213.1485	$213.15	$213.15	$213.10
Purchase #7	$40.96	4.706%	$42.8876	$42.89	$42.90	$42.90
7 purchase totals =	$901.23		$980.2977	$980.30	$980.30	$980.30