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	$143.41	10.105%	$157.9016	$157.90	$157.90	$157.90
Purchase #2	$245.39	4.681%	$256.8767	$256.88	$256.90	$256.90
Purchase #3	$26.42	6.393%	$28.109	$28.11	$28.10	$28.10
Purchase #4	$101.31	3.790%	$105.1496	$105.15	$105.15	$105.10
Purchase #5	$132.66	5.662%	$140.1712	$140.17	$140.15	$140.20
Purchase #6	$124.95	11.568%	$139.4042	$139.40	$139.40	$139.40
Purchase #7	$53.27	3.596%	$55.1856	$55.19	$55.20	$55.20
7 purchase totals =	$827.41		$882.7979	$882.80	$882.80	$882.80