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	$131.44	6.401%	$139.8535	$139.85	$139.85	$139.90
Purchase #2	$56.77	8.434%	$61.558	$61.56	$61.55	$61.60
Purchase #3	$57.58	3.700%	$59.7105	$59.71	$59.70	$59.70
Purchase #4	$23.43	13.529%	$26.5998	$26.60	$26.60	$26.60
Purchase #5	$238.97	9.849%	$262.5062	$262.51	$262.50	$262.50
Purchase #6	$32.41	5.191%	$34.0924	$34.09	$34.10	$34.10
Purchase #7	$78.60	5.472%	$82.901	$82.90	$82.90	$82.90
7 purchase totals =	$619.20		$667.2214	$667.22	$667.20	$667.30