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	$32.75	12.208%	$36.7481	$36.75	$36.75	$36.70
Purchase #2	$167.37	7.370%	$179.7052	$179.71	$179.70	$179.70
Purchase #3	$72.32	7.189%	$77.5191	$77.52	$77.50	$77.50
Purchase #4	$44.34	13.698%	$50.4137	$50.41	$50.40	$50.40
Purchase #5	$50.56	12.516%	$56.8881	$56.89	$56.90	$56.90
Purchase #6	$173.69	9.847%	$190.7933	$190.79	$190.80	$190.80
Purchase #7	$6.87	13.252%	$7.7804	$7.78	$7.80	$7.80
7 purchase totals =	$547.90		$599.8479	$599.85	$599.85	$599.80