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	$138.29	5.214%	$145.5004	$145.50	$145.50	$145.50
Purchase #2	$165.84	11.286%	$184.5567	$184.56	$184.55	$184.60
Purchase #3	$105.85	4.407%	$110.5148	$110.51	$110.50	$110.50
Purchase #4	$83.72	10.820%	$92.7785	$92.78	$92.80	$92.80
Purchase #5	$240.65	12.153%	$269.8962	$269.90	$269.90	$269.90
Purchase #6	$105.27	13.709%	$119.7015	$119.70	$119.70	$119.70
Purchase #7	$31.58	7.262%	$33.8733	$33.87	$33.85	$33.90
7 purchase totals =	$871.20		$956.8214	$956.82	$956.80	$956.90