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	$126.49	11.191%	$140.6455	$140.65	$140.65	$140.60
Purchase #2	$59.94	11.802%	$67.0141	$67.01	$67.00	$67.00
Purchase #3	$18.50	10.748%	$20.4884	$20.49	$20.50	$20.50
Purchase #4	$124.60	13.202%	$141.0497	$141.05	$141.05	$141.00
Purchase #5	$121.80	5.872%	$128.9521	$128.95	$128.95	$129.00
Purchase #6	$116.43	12.561%	$131.0548	$131.05	$131.05	$131.10
Purchase #7	$44.83	11.205%	$49.8532	$49.85	$49.85	$49.90
7 purchase totals =	$612.59		$679.0578	$679.05	$679.05	$679.10