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	$242.71	5.206%	$255.3455	$255.35	$255.35	$255.30
Purchase #2	$226.94	5.828%	$240.1661	$240.17	$240.15	$240.20
Purchase #3	$248.60	9.537%	$272.309	$272.31	$272.30	$272.30
Purchase #4	$203.59	13.467%	$231.0075	$231.01	$231.00	$231.00
Purchase #5	$39.63	7.138%	$42.4588	$42.46	$42.45	$42.50
Purchase #6	$194.50	13.797%	$221.3352	$221.34	$221.35	$221.30
Purchase #7	$172.72	6.469%	$183.8933	$183.89	$183.90	$183.90
7 purchase totals =	$1,328.69		$1,446.5154	$1,446.53	$1,446.50	$1,446.50