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	$150.81	4.714%	$157.9192	$157.92	$157.90	$157.90
Purchase #2	$37.66	13.753%	$42.8394	$42.84	$42.85	$42.80
Purchase #3	$175.49	9.315%	$191.8369	$191.84	$191.85	$191.80
Purchase #4	$151.77	9.145%	$165.6494	$165.65	$165.65	$165.60
Purchase #5	$132.83	4.395%	$138.6679	$138.67	$138.65	$138.70
Purchase #6	$25.31	8.500%	$27.4614	$27.46	$27.45	$27.50
Purchase #7	$241.73	12.442%	$271.806	$271.81	$271.80	$271.80
7 purchase totals =	$915.60		$996.1802	$996.19	$996.15	$996.10