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	$239.73	12.817%	$270.4562	$270.46	$270.45	$270.50
Purchase #2	$13.64	12.857%	$15.3937	$15.39	$15.40	$15.40
Purchase #3	$160.36	7.572%	$172.5025	$172.50	$172.50	$172.50
Purchase #4	$30.38	4.214%	$31.6602	$31.66	$31.65	$31.70
Purchase #5	$42.45	6.132%	$45.053	$45.05	$45.05	$45.10
Purchase #6	$107.78	12.699%	$121.467	$121.47	$121.45	$121.50
Purchase #7	$126.50	10.587%	$139.8926	$139.89	$139.90	$139.90
7 purchase totals =	$720.84		$796.4252	$796.42	$796.40	$796.60