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	$81.30	11.820%	$90.9097	$90.91	$90.90	$90.90
Purchase #2	$33.25	12.451%	$37.39	$37.39	$37.40	$37.40
Purchase #3	$217.53	5.571%	$229.6486	$229.65	$229.65	$229.60
Purchase #4	$85.50	11.427%	$95.2701	$95.27	$95.25	$95.30
Purchase #5	$77.81	9.701%	$85.3583	$85.36	$85.35	$85.40
Purchase #6	$105.43	13.827%	$120.0078	$120.01	$120.00	$120.00
Purchase #7	$232.79	10.859%	$258.0687	$258.07	$258.05	$258.10
7 purchase totals =	$833.61		$916.6532	$916.66	$916.60	$916.70