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	$81.27	9.719%	$89.1686	$89.17	$89.15	$89.20
Purchase #2	$159.84	6.187%	$169.7293	$169.73	$169.75	$169.70
Purchase #3	$15.29	8.544%	$16.5964	$16.60	$16.60	$16.60
Purchase #4	$53.50	10.439%	$59.0849	$59.08	$59.10	$59.10
Purchase #5	$217.61	12.358%	$244.5022	$244.50	$244.50	$244.50
Purchase #6	$105.49	13.311%	$119.5318	$119.53	$119.55	$119.50
Purchase #7	$245.52	4.583%	$256.7722	$256.77	$256.75	$256.80
7 purchase totals =	$878.52		$955.3854	$955.38	$955.40	$955.40