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	$57.79	6.796%	$61.7174	$61.72	$61.70	$61.70
Purchase #2	$237.71	6.796%	$253.8648	$253.86	$253.85	$253.90
Purchase #3	$71.76	3.790%	$74.4797	$74.48	$74.50	$74.50
Purchase #4	$40.46	13.343%	$45.8586	$45.86	$45.85	$45.90
Purchase #5	$45.65	5.433%	$48.1302	$48.13	$48.15	$48.10
Purchase #6	$35.63	6.306%	$37.8768	$37.88	$37.90	$37.90
Purchase #7	$143.96	4.481%	$150.4108	$150.41	$150.40	$150.40
7 purchase totals =	$632.96		$672.3383	$672.34	$672.35	$672.40