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	$55.69	5.786%	$58.9122	$58.91	$58.90	$58.90
Purchase #2	$224.88	13.751%	$255.8032	$255.80	$255.80	$255.80
Purchase #3	$205.56	11.675%	$229.5591	$229.56	$229.55	$229.60
Purchase #4	$34.55	8.531%	$37.4975	$37.50	$37.50	$37.50
Purchase #5	$222.62	8.795%	$242.1994	$242.20	$242.20	$242.20
Purchase #6	$178.90	11.706%	$199.842	$199.84	$199.85	$199.80
Purchase #7	$62.51	12.230%	$70.155	$70.16	$70.15	$70.20
7 purchase totals =	$984.71		$1,093.9684	$1,093.97	$1,093.95	$1,094.00