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	$121.89	4.510%	$127.3872	$127.39	$127.40	$127.40
Purchase #2	$57.86	11.784%	$64.6782	$64.68	$64.70	$64.70
Purchase #3	$105.53	3.123%	$108.8257	$108.83	$108.85	$108.80
Purchase #4	$97.59	12.505%	$109.7936	$109.79	$109.80	$109.80
Purchase #5	$128.80	9.848%	$141.4842	$141.48	$141.50	$141.50
Purchase #6	$111.55	10.761%	$123.5539	$123.55	$123.55	$123.60
Purchase #7	$23.67	12.325%	$26.5873	$26.59	$26.60	$26.60
7 purchase totals =	$646.89		$702.3101	$702.31	$702.40	$702.40