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	$6.65	5.805%	$7.036	$7.04	$7.05	$7.00
Purchase #2	$175.25	12.367%	$196.9232	$196.92	$196.90	$196.90
Purchase #3	$7.54	10.333%	$8.3191	$8.32	$8.30	$8.30
Purchase #4	$128.87	13.452%	$146.2056	$146.21	$146.20	$146.20
Purchase #5	$147.35	3.311%	$152.2288	$152.23	$152.25	$152.20
Purchase #6	$152.47	8.669%	$165.6876	$165.69	$165.70	$165.70
Purchase #7	$224.62	10.176%	$247.4773	$247.48	$247.50	$247.50
7 purchase totals =	$842.75		$923.8776	$923.89	$923.90	$923.80