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	$27.28	11.834%	$30.5083	$30.51	$30.50	$30.50
Purchase #2	$250.54	12.485%	$281.8199	$281.82	$281.80	$281.80
Purchase #3	$132.47	3.335%	$136.8879	$136.89	$136.90	$136.90
Purchase #4	$215.39	12.598%	$242.5248	$242.52	$242.50	$242.50
Purchase #5	$20.46	3.219%	$21.1186	$21.12	$21.10	$21.10
Purchase #6	$112.33	11.708%	$125.4816	$125.48	$125.50	$125.50
Purchase #7	$161.75	7.390%	$173.7033	$173.70	$173.70	$173.70
7 purchase totals =	$920.22		$1,012.0444	$1,012.04	$1,012.00	$1,012.00