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	$113.94	12.247%	$127.8942	$127.89	$127.90	$127.90
Purchase #2	$185.32	12.353%	$208.2126	$208.21	$208.20	$208.20
Purchase #3	$250.57	9.271%	$273.8003	$273.80	$273.80	$273.80
Purchase #4	$10.77	10.155%	$11.8637	$11.86	$11.85	$11.90
Purchase #5	$35.76	9.533%	$39.169	$39.17	$39.15	$39.20
Purchase #6	$75.69	6.363%	$80.5062	$80.51	$80.50	$80.50
Purchase #7	$33.86	7.143%	$36.2786	$36.28	$36.30	$36.30
7 purchase totals =	$705.91		$777.7246	$777.72	$777.70	$777.80