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	$250.51	13.677%	$284.7723	$284.77	$284.75	$284.80
Purchase #2	$222.54	13.341%	$252.2291	$252.23	$252.25	$252.20
Purchase #3	$108.69	7.424%	$116.7591	$116.76	$116.75	$116.80
Purchase #4	$80.98	5.176%	$85.1715	$85.17	$85.15	$85.20
Purchase #5	$173.38	8.676%	$188.4224	$188.42	$188.40	$188.40
Purchase #6	$88.90	11.706%	$99.3066	$99.31	$99.30	$99.30
Purchase #7	$99.56	4.165%	$103.7067	$103.71	$103.70	$103.70
7 purchase totals =	$1,024.56		$1,130.3677	$1,130.37	$1,130.30	$1,130.40