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	$132.88	5.758%	$140.5312	$140.53	$140.55	$140.50
Purchase #2	$72.47	5.211%	$76.2464	$76.25	$76.25	$76.20
Purchase #3	$40.82	8.730%	$44.3836	$44.38	$44.40	$44.40
Purchase #4	$52.80	12.178%	$59.23	$59.23	$59.25	$59.20
Purchase #5	$61.43	11.202%	$68.3114	$68.31	$68.30	$68.30
Purchase #6	$78.86	12.648%	$88.8342	$88.83	$88.85	$88.80
Purchase #7	$25.67	8.114%	$27.7529	$27.75	$27.75	$27.80
7 purchase totals =	$464.93		$505.2897	$505.28	$505.35	$505.20