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	$137.65	10.578%	$152.2106	$152.21	$152.20	$152.20
Purchase #2	$106.32	13.658%	$120.8412	$120.84	$120.85	$120.80
Purchase #3	$91.58	9.142%	$99.9522	$99.95	$99.95	$100.00
Purchase #4	$195.80	10.513%	$216.3845	$216.38	$216.40	$216.40
Purchase #5	$242.56	13.753%	$275.9193	$275.92	$275.90	$275.90
Purchase #6	$54.35	8.412%	$58.9219	$58.92	$58.90	$58.90
Purchase #7	$82.43	12.668%	$92.8722	$92.87	$92.85	$92.90
7 purchase totals =	$910.69		$1,017.1019	$1,017.09	$1,017.05	$1,017.10