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	$131.46	11.315%	$146.3347	$146.33	$146.35	$146.30
Purchase #2	$169.75	8.816%	$184.7152	$184.72	$184.70	$184.70
Purchase #3	$206.33	10.683%	$228.3722	$228.37	$228.35	$228.40
Purchase #4	$239.66	12.850%	$270.4563	$270.46	$270.45	$270.50
Purchase #5	$23.54	12.667%	$26.5218	$26.52	$26.50	$26.50
Purchase #6	$219.53	13.818%	$249.8647	$249.86	$249.85	$249.90
Purchase #7	$63.39	4.570%	$66.2869	$66.29	$66.30	$66.30
7 purchase totals =	$1,053.66		$1,172.5518	$1,172.55	$1,172.50	$1,172.60