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	$96.35	3.162%	$99.3966	$99.40	$99.40	$99.40
Purchase #2	$113.49	5.855%	$120.1348	$120.13	$120.15	$120.10
Purchase #3	$65.87	13.198%	$74.5635	$74.56	$74.55	$74.60
Purchase #4	$95.81	5.775%	$101.343	$101.34	$101.35	$101.30
Purchase #5	$61.42	9.378%	$67.18	$67.18	$67.20	$67.20
Purchase #6	$22.89	8.339%	$24.7988	$24.80	$24.80	$24.80
Purchase #7	$65.69	10.369%	$72.5014	$72.50	$72.50	$72.50
7 purchase totals =	$521.52		$559.9181	$559.91	$559.95	$559.90