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	$41.90	6.530%	$44.6361	$44.64	$44.65	$44.60
Purchase #2	$77.28	4.138%	$80.4778	$80.48	$80.50	$80.50
Purchase #3	$71.49	7.855%	$77.1055	$77.11	$77.10	$77.10
Purchase #4	$61.60	4.229%	$64.2051	$64.21	$64.20	$64.20
Purchase #5	$78.76	9.733%	$86.4257	$86.43	$86.45	$86.40
Purchase #6	$50.64	13.766%	$57.6111	$57.61	$57.60	$57.60
Purchase #7	$166.48	7.165%	$178.4083	$178.41	$178.40	$178.40
7 purchase totals =	$548.15		$588.8696	$588.89	$588.90	$588.80