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	$10.90	5.379%	$11.4863	$11.49	$11.50	$11.50
Purchase #2	$149.86	7.304%	$160.8058	$160.81	$160.80	$160.80
Purchase #3	$195.70	13.448%	$222.0177	$222.02	$222.00	$222.00
Purchase #4	$240.60	13.810%	$273.8269	$273.83	$273.85	$273.80
Purchase #5	$200.25	11.654%	$223.5871	$223.59	$223.60	$223.60
Purchase #6	$197.33	8.211%	$213.5328	$213.53	$213.55	$213.50
Purchase #7	$194.82	8.853%	$212.0674	$212.07	$212.05	$212.10
7 purchase totals =	$1,189.46		$1,317.3240	$1,317.34	$1,317.35	$1,317.30