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	$85.32	7.634%	$91.8333	$91.83	$91.85	$91.80
Purchase #2	$83.53	8.754%	$90.8422	$90.84	$90.85	$90.80
Purchase #3	$22.59	11.309%	$25.1447	$25.14	$25.15	$25.10
Purchase #4	$29.91	10.134%	$32.9411	$32.94	$32.95	$32.90
Purchase #5	$124.95	7.707%	$134.5799	$134.58	$134.60	$134.60
Purchase #6	$199.96	9.577%	$219.1102	$219.11	$219.10	$219.10
Purchase #7	$187.75	4.579%	$196.3471	$196.35	$196.35	$196.30
7 purchase totals =	$734.01		$790.7985	$790.79	$790.85	$790.60