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	$81.59	11.398%	$90.8896	$90.89	$90.90	$90.90
Purchase #2	$140.54	8.347%	$152.2709	$152.27	$152.25	$152.30
Purchase #3	$45.32	11.816%	$50.675	$50.68	$50.70	$50.70
Purchase #4	$17.58	3.279%	$18.1564	$18.16	$18.15	$18.20
Purchase #5	$61.95	3.370%	$64.0377	$64.04	$64.05	$64.00
Purchase #6	$186.97	4.249%	$194.9144	$194.91	$194.90	$194.90
Purchase #7	$134.53	9.243%	$146.9646	$146.96	$146.95	$147.00
7 purchase totals =	$668.48		$717.9086	$717.91	$717.90	$718.00