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	$179.58	3.172%	$185.2763	$185.28	$185.30	$185.30
Purchase #2	$223.86	7.753%	$241.2159	$241.22	$241.20	$241.20
Purchase #3	$95.89	9.210%	$104.7215	$104.72	$104.70	$104.70
Purchase #4	$202.54	9.857%	$222.5044	$222.50	$222.50	$222.50
Purchase #5	$122.57	12.192%	$137.5137	$137.51	$137.50	$137.50
Purchase #6	$214.30	12.136%	$240.3074	$240.31	$240.30	$240.30
Purchase #7	$128.75	3.334%	$133.0425	$133.04	$133.05	$133.00
7 purchase totals =	$1,167.49		$1,264.5817	$1,264.58	$1,264.55	$1,264.50