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	$81.52	11.502%	$90.8964	$90.90	$90.90	$90.90
Purchase #2	$29.78	4.560%	$31.138	$31.14	$31.15	$31.10
Purchase #3	$80.33	13.512%	$91.1842	$91.18	$91.20	$91.20
Purchase #4	$91.74	8.328%	$99.3801	$99.38	$99.40	$99.40
Purchase #5	$227.44	10.428%	$251.1574	$251.16	$251.15	$251.20
Purchase #6	$188.85	10.707%	$209.0702	$209.07	$209.05	$209.10
Purchase #7	$53.84	13.737%	$61.236	$61.24	$61.25	$61.20
7 purchase totals =	$753.50		$834.0623	$834.07	$834.10	$834.10