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	$22.74	13.332%	$25.7717	$25.77	$25.75	$25.80
Purchase #2	$126.93	11.729%	$141.8176	$141.82	$141.80	$141.80
Purchase #3	$192.90	13.803%	$219.526	$219.53	$219.55	$219.50
Purchase #4	$90.57	11.285%	$100.7908	$100.79	$100.80	$100.80
Purchase #5	$124.26	11.617%	$138.6953	$138.70	$138.70	$138.70
Purchase #6	$59.70	13.688%	$67.8717	$67.87	$67.85	$67.90
Purchase #7	$123.42	13.244%	$139.7657	$139.77	$139.75	$139.80
7 purchase totals =	$740.52		$834.2388	$834.25	$834.20	$834.30