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	$50.46	6.541%	$53.7606	$53.76	$53.75	$53.80
Purchase #2	$198.26	3.419%	$205.0385	$205.04	$205.05	$205.00
Purchase #3	$48.94	5.178%	$51.4741	$51.47	$51.45	$51.50
Purchase #4	$84.60	7.103%	$90.6091	$90.61	$90.60	$90.60
Purchase #5	$114.33	13.584%	$129.8606	$129.86	$129.85	$129.90
Purchase #6	$48.61	3.130%	$50.1315	$50.13	$50.15	$50.10
Purchase #7	$83.90	8.546%	$91.0701	$91.07	$91.05	$91.10
7 purchase totals =	$629.10		$671.9445	$671.94	$671.90	$672.00