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	$37.71	13.765%	$42.9008	$42.90	$42.90	$42.90
Purchase #2	$144.57	3.874%	$150.1706	$150.17	$150.15	$150.20
Purchase #3	$48.36	4.208%	$50.395	$50.40	$50.40	$50.40
Purchase #4	$79.56	8.601%	$86.403	$86.40	$86.40	$86.40
Purchase #5	$64.70	3.790%	$67.1521	$67.15	$67.15	$67.20
Purchase #6	$170.29	3.545%	$176.3268	$176.33	$176.35	$176.30
Purchase #7	$9.72	5.510%	$10.2556	$10.26	$10.25	$10.30
7 purchase totals =	$554.91		$583.6039	$583.61	$583.60	$583.70