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	$91.95	7.846%	$99.1644	$99.16	$99.15	$99.20
Purchase #2	$77.74	4.661%	$81.3635	$81.36	$81.35	$81.40
Purchase #3	$249.31	10.662%	$275.8914	$275.89	$275.90	$275.90
Purchase #4	$115.36	4.442%	$120.4843	$120.48	$120.50	$120.50
Purchase #5	$111.58	10.375%	$123.1564	$123.16	$123.15	$123.20
Purchase #6	$214.36	13.459%	$243.2107	$243.21	$243.20	$243.20
Purchase #7	$152.47	13.406%	$172.9101	$172.91	$172.90	$172.90
7 purchase totals =	$1,012.77		$1,116.1808	$1,116.17	$1,116.15	$1,116.30