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	$199.61	13.189%	$225.9366	$225.94	$225.95	$225.90
Purchase #2	$229.99	13.113%	$260.1486	$260.15	$260.15	$260.10
Purchase #3	$205.92	12.405%	$231.4644	$231.46	$231.45	$231.50
Purchase #4	$226.64	10.256%	$249.8842	$249.88	$249.90	$249.90
Purchase #5	$226.96	10.518%	$250.8317	$250.83	$250.85	$250.80
Purchase #6	$166.88	9.348%	$182.4799	$182.48	$182.50	$182.50
Purchase #7	$82.45	10.332%	$90.9687	$90.97	$90.95	$91.00
7 purchase totals =	$1,338.45		$1,491.7141	$1,491.71	$1,491.75	$1,491.70