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	$94.61	5.345%	$99.6669	$99.67	$99.65	$99.70
Purchase #2	$48.41	12.539%	$54.4801	$54.48	$54.50	$54.50
Purchase #3	$173.57	8.585%	$188.471	$188.47	$188.45	$188.50
Purchase #4	$91.48	12.425%	$102.8464	$102.85	$102.85	$102.80
Purchase #5	$132.79	5.364%	$139.9129	$139.91	$139.90	$139.90
Purchase #6	$153.86	10.663%	$170.2661	$170.27	$170.25	$170.30
Purchase #7	$111.44	4.560%	$116.5217	$116.52	$116.50	$116.50
7 purchase totals =	$806.16		$872.1651	$872.17	$872.10	$872.20