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	$155.79	12.392%	$175.0955	$175.10	$175.10	$175.10
Purchase #2	$107.34	11.582%	$119.7721	$119.77	$119.75	$119.80
Purchase #3	$141.54	6.624%	$150.9156	$150.92	$150.90	$150.90
Purchase #4	$111.80	6.805%	$119.408	$119.41	$119.40	$119.40
Purchase #5	$108.43	3.145%	$111.8401	$111.84	$111.85	$111.80
Purchase #6	$133.64	8.448%	$144.9299	$144.93	$144.95	$144.90
Purchase #7	$11.34	13.724%	$12.8963	$12.90	$12.90	$12.90
7 purchase totals =	$769.88		$834.8575	$834.87	$834.85	$834.80