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	$89.92	4.202%	$93.6984	$93.70	$93.70	$93.70
Purchase #2	$39.68	6.198%	$42.1394	$42.14	$42.15	$42.10
Purchase #3	$185.59	12.702%	$209.1636	$209.16	$209.15	$209.20
Purchase #4	$123.74	13.479%	$140.4189	$140.42	$140.40	$140.40
Purchase #5	$39.56	7.733%	$42.6192	$42.62	$42.60	$42.60
Purchase #6	$151.88	5.347%	$160.001	$160.00	$160.00	$160.00
Purchase #7	$72.58	7.491%	$78.017	$78.02	$78.00	$78.00
7 purchase totals =	$702.95		$766.0575	$766.06	$766.00	$766.00