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	$176.57	12.689%	$198.975	$198.98	$199.00	$199.00
Purchase #2	$135.75	12.594%	$152.8464	$152.85	$152.85	$152.80
Purchase #3	$108.65	13.120%	$122.9049	$122.90	$122.90	$122.90
Purchase #4	$40.45	12.526%	$45.5168	$45.52	$45.50	$45.50
Purchase #5	$112.53	3.510%	$116.4798	$116.48	$116.50	$116.50
Purchase #6	$122.49	11.733%	$136.8618	$136.86	$136.85	$136.90
Purchase #7	$136.39	8.811%	$148.4073	$148.41	$148.40	$148.40
7 purchase totals =	$832.83		$921.9920	$922.00	$922.00	$922.00