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	$231.45	12.501%	$260.3836	$260.38	$260.40	$260.40
Purchase #2	$201.82	11.251%	$224.5268	$224.53	$224.55	$224.50
Purchase #3	$190.75	8.308%	$206.5975	$206.60	$206.60	$206.60
Purchase #4	$87.64	12.607%	$98.6888	$98.69	$98.70	$98.70
Purchase #5	$76.95	11.539%	$85.8293	$85.83	$85.85	$85.80
Purchase #6	$90.99	10.848%	$100.8606	$100.86	$100.85	$100.90
Purchase #7	$36.42	11.609%	$40.648	$40.65	$40.65	$40.60
7 purchase totals =	$916.02		$1,017.5346	$1,017.54	$1,017.60	$1,017.50