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	$61.73	7.797%	$66.5431	$66.54	$66.55	$66.50
Purchase #2	$93.91	5.491%	$99.0666	$99.07	$99.05	$99.10
Purchase #3	$165.59	8.332%	$179.387	$179.39	$179.40	$179.40
Purchase #4	$151.87	11.210%	$168.8946	$168.89	$168.90	$168.90
Purchase #5	$125.98	8.240%	$136.3608	$136.36	$136.35	$136.40
Purchase #6	$119.28	4.358%	$124.4782	$124.48	$124.50	$124.50
Purchase #7	$94.31	12.120%	$105.7404	$105.74	$105.75	$105.70
7 purchase totals =	$812.67		$880.4707	$880.47	$880.50	$880.50