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	$35.70	13.632%	$40.5666	$40.57	$40.55	$40.60
Purchase #2	$88.51	5.148%	$93.0665	$93.07	$93.05	$93.10
Purchase #3	$173.64	9.661%	$190.4154	$190.42	$190.40	$190.40
Purchase #4	$143.28	6.382%	$152.4241	$152.42	$152.40	$152.40
Purchase #5	$148.90	10.638%	$164.74	$164.74	$164.75	$164.70
Purchase #6	$93.96	7.111%	$100.6415	$100.64	$100.65	$100.60
Purchase #7	$232.87	10.282%	$256.8137	$256.81	$256.80	$256.80
7 purchase totals =	$916.86		$998.6678	$998.67	$998.60	$998.60