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	$149.95	9.620%	$164.3752	$164.38	$164.40	$164.40
Purchase #2	$229.72	8.648%	$249.5862	$249.59	$249.60	$249.60
Purchase #3	$175.60	7.797%	$189.2915	$189.29	$189.30	$189.30
Purchase #4	$225.95	7.435%	$242.7494	$242.75	$242.75	$242.70
Purchase #5	$180.38	5.781%	$190.8078	$190.81	$190.80	$190.80
Purchase #6	$242.77	7.268%	$260.4145	$260.41	$260.40	$260.40
Purchase #7	$37.52	12.649%	$42.2659	$42.27	$42.25	$42.30
7 purchase totals =	$1,241.89		$1,339.4905	$1,339.50	$1,339.50	$1,339.50