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	$75.50	3.806%	$78.3735	$78.37	$78.35	$78.40
Purchase #2	$247.82	6.771%	$264.5999	$264.60	$264.60	$264.60
Purchase #3	$70.61	11.624%	$78.8177	$78.82	$78.80	$78.80
Purchase #4	$241.63	7.460%	$259.6556	$259.66	$259.65	$259.70
Purchase #5	$45.37	6.833%	$48.4701	$48.47	$48.45	$48.50
Purchase #6	$76.87	7.115%	$82.3393	$82.34	$82.35	$82.30
Purchase #7	$129.41	10.761%	$143.3358	$143.34	$143.35	$143.30
7 purchase totals =	$887.21		$955.5919	$955.60	$955.55	$955.60