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	$250.72	8.839%	$272.8811	$272.88	$272.90	$272.90
Purchase #2	$210.34	3.114%	$216.89	$216.89	$216.90	$216.90
Purchase #3	$183.71	7.140%	$196.8269	$196.83	$196.85	$196.80
Purchase #4	$27.51	4.540%	$28.759	$28.76	$28.75	$28.80
Purchase #5	$231.80	8.620%	$251.7812	$251.78	$251.80	$251.80
Purchase #6	$95.45	13.689%	$108.5162	$108.52	$108.50	$108.50
Purchase #7	$189.87	8.581%	$206.1627	$206.16	$206.15	$206.20
7 purchase totals =	$1,189.40		$1,281.8171	$1,281.82	$1,281.85	$1,281.90