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	$109.89	10.495%	$121.423	$121.42	$121.40	$121.40
Purchase #2	$95.77	5.281%	$100.8276	$100.83	$100.85	$100.80
Purchase #3	$54.82	12.772%	$61.8216	$61.82	$61.80	$61.80
Purchase #4	$222.70	6.513%	$237.2045	$237.20	$237.20	$237.20
Purchase #5	$95.33	11.472%	$106.2663	$106.27	$106.25	$106.30
Purchase #6	$216.35	11.573%	$241.3882	$241.39	$241.40	$241.40
Purchase #7	$68.73	13.841%	$78.2429	$78.24	$78.25	$78.20
7 purchase totals =	$863.59		$947.1741	$947.17	$947.15	$947.10