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	$130.47	5.139%	$137.1749	$137.17	$137.15	$137.20
Purchase #2	$185.68	8.178%	$200.8649	$200.86	$200.85	$200.90
Purchase #3	$38.71	3.761%	$40.1659	$40.17	$40.15	$40.20
Purchase #4	$82.86	8.559%	$89.952	$89.95	$89.95	$90.00
Purchase #5	$223.81	13.396%	$253.7916	$253.79	$253.80	$253.80
Purchase #6	$131.56	9.584%	$144.1687	$144.17	$144.15	$144.20
Purchase #7	$28.59	5.355%	$30.121	$30.12	$30.10	$30.10
7 purchase totals =	$821.68		$896.2390	$896.23	$896.15	$896.40