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	$47.33	11.382%	$52.7171	$52.72	$52.70	$52.70
Purchase #2	$216.45	4.487%	$226.1621	$226.16	$226.15	$226.20
Purchase #3	$95.33	9.367%	$104.2596	$104.26	$104.25	$104.30
Purchase #4	$153.89	12.272%	$172.7754	$172.78	$172.80	$172.80
Purchase #5	$89.34	4.136%	$93.0351	$93.04	$93.05	$93.00
Purchase #6	$158.51	5.648%	$167.4626	$167.46	$167.45	$167.50
Purchase #7	$31.53	7.241%	$33.8131	$33.81	$33.80	$33.80
7 purchase totals =	$792.38		$850.2250	$850.23	$850.20	$850.30