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	$250.50	11.192%	$278.536	$278.54	$278.55	$278.50
Purchase #2	$242.90	5.196%	$255.5211	$255.52	$255.50	$255.50
Purchase #3	$155.74	3.202%	$160.7268	$160.73	$160.75	$160.70
Purchase #4	$171.89	8.451%	$186.4164	$186.42	$186.40	$186.40
Purchase #5	$87.44	13.860%	$99.5592	$99.56	$99.55	$99.60
Purchase #6	$205.53	5.268%	$216.3573	$216.36	$216.35	$216.40
Purchase #7	$84.53	13.422%	$95.8756	$95.88	$95.90	$95.90
7 purchase totals =	$1,198.53		$1,292.9924	$1,293.01	$1,293.00	$1,293.00