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	$99.63	11.638%	$111.2249	$111.22	$111.20	$111.20
Purchase #2	$93.94	11.547%	$104.7873	$104.79	$104.80	$104.80
Purchase #3	$142.77	9.644%	$156.5387	$156.54	$156.55	$156.50
Purchase #4	$9.66	13.334%	$10.9481	$10.95	$10.95	$10.90
Purchase #5	$33.72	8.270%	$36.5086	$36.51	$36.50	$36.50
Purchase #6	$37.64	7.723%	$40.5469	$40.55	$40.55	$40.50
Purchase #7	$137.58	11.210%	$153.0027	$153.00	$153.00	$153.00
7 purchase totals =	$554.94		$613.5572	$613.56	$613.55	$613.40