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	$120.96	4.358%	$126.2314	$126.23	$126.25	$126.20
Purchase #2	$37.67	7.265%	$40.4067	$40.41	$40.40	$40.40
Purchase #3	$32.37	3.575%	$33.5272	$33.53	$33.55	$33.50
Purchase #4	$87.68	12.140%	$98.3244	$98.32	$98.30	$98.30
Purchase #5	$25.32	12.472%	$28.4779	$28.48	$28.50	$28.50
Purchase #6	$77.43	5.243%	$81.4897	$81.49	$81.50	$81.50
Purchase #7	$78.95	7.129%	$84.5783	$84.58	$84.60	$84.60
7 purchase totals =	$460.38		$493.0356	$493.04	$493.10	$493.00