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	$135.46	9.380%	$148.1661	$148.17	$148.15	$148.20
Purchase #2	$229.89	9.500%	$251.7296	$251.73	$251.75	$251.70
Purchase #3	$242.34	12.214%	$271.9394	$271.94	$271.95	$271.90
Purchase #4	$24.68	10.797%	$27.3447	$27.34	$27.35	$27.30
Purchase #5	$56.83	4.710%	$59.5067	$59.51	$59.50	$59.50
Purchase #6	$18.42	13.146%	$20.8415	$20.84	$20.85	$20.80
Purchase #7	$88.56	5.547%	$93.4724	$93.47	$93.45	$93.50
7 purchase totals =	$796.18		$873.0004	$873.00	$873.00	$872.90