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	$130.72	13.608%	$148.5084	$148.51	$148.50	$148.50
Purchase #2	$241.89	6.206%	$256.9017	$256.90	$256.90	$256.90
Purchase #3	$12.52	10.179%	$13.7944	$13.79	$13.80	$13.80
Purchase #4	$58.67	7.653%	$63.16	$63.16	$63.15	$63.20
Purchase #5	$175.34	11.477%	$195.4638	$195.46	$195.45	$195.50
Purchase #6	$181.84	9.186%	$198.5438	$198.54	$198.55	$198.50
Purchase #7	$50.99	7.503%	$54.8158	$54.82	$54.80	$54.80
7 purchase totals =	$851.97		$931.1879	$931.18	$931.15	$931.20