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	$37.78	4.559%	$39.5024	$39.50	$39.50	$39.50
Purchase #2	$88.56	12.793%	$99.8895	$99.89	$99.90	$99.90
Purchase #3	$238.71	3.255%	$246.48	$246.48	$246.50	$246.50
Purchase #4	$80.35	5.495%	$84.7652	$84.77	$84.75	$84.80
Purchase #5	$201.30	7.650%	$216.6995	$216.70	$216.70	$216.70
Purchase #6	$85.85	4.365%	$89.5974	$89.60	$89.60	$89.60
Purchase #7	$241.53	6.371%	$256.9179	$256.92	$256.90	$256.90
7 purchase totals =	$974.08		$1,033.8519	$1,033.86	$1,033.85	$1,033.90