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	$113.82	4.120%	$118.5094	$118.51	$118.50	$118.50
Purchase #2	$68.61	4.444%	$71.659	$71.66	$71.65	$71.70
Purchase #3	$249.87	13.413%	$283.3851	$283.39	$283.40	$283.40
Purchase #4	$111.38	10.189%	$122.7285	$122.73	$122.75	$122.70
Purchase #5	$104.63	7.825%	$112.8173	$112.82	$112.80	$112.80
Purchase #6	$75.31	10.822%	$83.46	$83.46	$83.45	$83.50
Purchase #7	$35.97	12.594%	$40.5001	$40.50	$40.50	$40.50
7 purchase totals =	$759.59		$833.0594	$833.07	$833.05	$833.10