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	$128.31	5.481%	$135.3427	$135.34	$135.35	$135.30
Purchase #2	$216.62	12.659%	$244.0419	$244.04	$244.05	$244.00
Purchase #3	$210.96	5.388%	$222.3265	$222.33	$222.35	$222.30
Purchase #4	$28.67	13.352%	$32.498	$32.50	$32.50	$32.50
Purchase #5	$174.58	9.605%	$191.3484	$191.35	$191.35	$191.30
Purchase #6	$181.82	10.142%	$200.2602	$200.26	$200.25	$200.30
Purchase #7	$182.75	11.337%	$203.4684	$203.47	$203.45	$203.50
7 purchase totals =	$1,123.71		$1,229.2861	$1,229.29	$1,229.30	$1,229.20