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	$138.94	6.645%	$148.1726	$148.17	$148.15	$148.20
Purchase #2	$19.53	6.871%	$20.8719	$20.87	$20.85	$20.90
Purchase #3	$94.83	13.347%	$107.487	$107.49	$107.50	$107.50
Purchase #4	$172.89	6.606%	$184.3111	$184.31	$184.30	$184.30
Purchase #5	$19.81	5.790%	$20.957	$20.96	$20.95	$21.00
Purchase #6	$79.40	5.388%	$83.6781	$83.68	$83.70	$83.70
Purchase #7	$75.81	10.105%	$83.4706	$83.47	$83.45	$83.50
7 purchase totals =	$601.21		$648.9483	$648.95	$648.90	$649.10