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	$100.53	10.700%	$111.2867	$111.29	$111.30	$111.30
Purchase #2	$69.94	11.732%	$78.1454	$78.15	$78.15	$78.10
Purchase #3	$97.40	9.587%	$106.7377	$106.74	$106.75	$106.70
Purchase #4	$70.86	3.522%	$73.3557	$73.36	$73.35	$73.40
Purchase #5	$198.42	11.773%	$221.78	$221.78	$221.80	$221.80
Purchase #6	$32.57	12.341%	$36.5895	$36.59	$36.60	$36.60
Purchase #7	$131.50	4.864%	$137.8962	$137.90	$137.90	$137.90
7 purchase totals =	$701.22		$765.7912	$765.81	$765.85	$765.80