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	$234.37	8.166%	$253.5087	$253.51	$253.50	$253.50
Purchase #2	$214.39	5.342%	$225.8427	$225.84	$225.85	$225.80
Purchase #3	$124.93	4.814%	$130.9441	$130.94	$130.95	$130.90
Purchase #4	$185.79	12.451%	$208.9227	$208.92	$208.90	$208.90
Purchase #5	$131.73	8.867%	$143.4105	$143.41	$143.40	$143.40
Purchase #6	$103.75	7.269%	$111.2916	$111.29	$111.30	$111.30
Purchase #7	$233.31	5.860%	$246.982	$246.98	$247.00	$247.00
7 purchase totals =	$1,228.27		$1,320.9023	$1,320.89	$1,320.90	$1,320.80