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	$82.83	9.643%	$90.8173	$90.82	$90.80	$90.80
Purchase #2	$56.88	3.610%	$58.9334	$58.93	$58.95	$58.90
Purchase #3	$175.73	13.154%	$198.8455	$198.85	$198.85	$198.80
Purchase #4	$187.34	9.800%	$205.6993	$205.70	$205.70	$205.70
Purchase #5	$180.61	10.301%	$199.2146	$199.21	$199.20	$199.20
Purchase #6	$33.72	7.220%	$36.1546	$36.15	$36.15	$36.20
Purchase #7	$204.38	7.570%	$219.8516	$219.85	$219.85	$219.90
7 purchase totals =	$921.49		$1,009.5163	$1,009.51	$1,009.50	$1,009.50