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	$99.84	5.768%	$105.5988	$105.60	$105.60	$105.60
Purchase #2	$116.52	8.594%	$126.5337	$126.53	$126.55	$126.50
Purchase #3	$201.28	11.333%	$224.0911	$224.09	$224.10	$224.10
Purchase #4	$79.53	4.500%	$83.1089	$83.11	$83.10	$83.10
Purchase #5	$78.84	8.787%	$85.7677	$85.77	$85.75	$85.80
Purchase #6	$31.37	5.614%	$33.1311	$33.13	$33.15	$33.10
Purchase #7	$14.50	7.448%	$15.58	$15.58	$15.60	$15.60
7 purchase totals =	$621.88		$673.8113	$673.81	$673.85	$673.80