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	$59.93	11.492%	$66.8172	$66.82	$66.80	$66.80
Purchase #2	$37.58	10.118%	$41.3823	$41.38	$41.40	$41.40
Purchase #3	$60.52	12.119%	$67.8544	$67.85	$67.85	$67.90
Purchase #4	$92.66	10.785%	$102.6534	$102.65	$102.65	$102.70
Purchase #5	$72.55	8.292%	$78.5658	$78.57	$78.55	$78.60
Purchase #6	$76.59	6.389%	$81.4833	$81.48	$81.50	$81.50
Purchase #7	$105.51	12.679%	$118.8876	$118.89	$118.90	$118.90
7 purchase totals =	$505.34		$557.6440	$557.64	$557.65	$557.80