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	$31.43	6.632%	$33.5144	$33.51	$33.50	$33.50
Purchase #2	$100.65	5.133%	$105.8164	$105.82	$105.80	$105.80
Purchase #3	$170.62	3.516%	$176.619	$176.62	$176.60	$176.60
Purchase #4	$85.39	11.545%	$95.2483	$95.25	$95.25	$95.20
Purchase #5	$209.74	6.239%	$222.8257	$222.83	$222.85	$222.80
Purchase #6	$171.53	10.518%	$189.5715	$189.57	$189.55	$189.60
Purchase #7	$23.83	3.719%	$24.7162	$24.72	$24.70	$24.70
7 purchase totals =	$793.19		$848.3115	$848.32	$848.25	$848.20