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	$219.77	4.272%	$229.1586	$229.16	$229.15	$229.20
Purchase #2	$234.72	6.386%	$249.7092	$249.71	$249.70	$249.70
Purchase #3	$117.86	8.731%	$128.1504	$128.15	$128.15	$128.20
Purchase #4	$40.91	4.731%	$42.8455	$42.85	$42.85	$42.80
Purchase #5	$31.47	5.560%	$33.2197	$33.22	$33.20	$33.20
Purchase #6	$9.77	4.233%	$10.1836	$10.18	$10.20	$10.20
Purchase #7	$18.64	13.689%	$21.1916	$21.19	$21.20	$21.20
7 purchase totals =	$673.14		$714.4586	$714.46	$714.45	$714.50