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	$163.92	12.544%	$184.4821	$184.48	$184.50	$184.50
Purchase #2	$85.54	9.742%	$93.8733	$93.87	$93.85	$93.90
Purchase #3	$99.87	12.198%	$112.0521	$112.05	$112.05	$112.10
Purchase #4	$152.74	11.530%	$170.3509	$170.35	$170.35	$170.40
Purchase #5	$33.25	10.575%	$36.7662	$36.77	$36.75	$36.80
Purchase #6	$90.29	10.533%	$99.8002	$99.80	$99.80	$99.80
Purchase #7	$86.72	4.708%	$90.8028	$90.80	$90.80	$90.80
7 purchase totals =	$712.33		$788.1276	$788.12	$788.10	$788.30