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	$82.55	9.643%	$90.5103	$90.51	$90.50	$90.50
Purchase #2	$92.98	5.806%	$98.3784	$98.38	$98.40	$98.40
Purchase #3	$179.90	5.446%	$189.6974	$189.70	$189.70	$189.70
Purchase #4	$205.81	7.817%	$221.8982	$221.90	$221.90	$221.90
Purchase #5	$98.77	8.165%	$106.8346	$106.83	$106.85	$106.80
Purchase #6	$215.26	6.698%	$229.6781	$229.68	$229.70	$229.70
Purchase #7	$11.77	6.596%	$12.5463	$12.55	$12.55	$12.50
7 purchase totals =	$887.04		$949.5433	$949.55	$949.60	$949.50