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	$42.54	13.114%	$48.1187	$48.12	$48.10	$48.10
Purchase #2	$38.51	8.754%	$41.8812	$41.88	$41.90	$41.90
Purchase #3	$175.37	4.639%	$183.5054	$183.51	$183.50	$183.50
Purchase #4	$211.26	4.565%	$220.904	$220.90	$220.90	$220.90
Purchase #5	$100.91	10.583%	$111.5893	$111.59	$111.60	$111.60
Purchase #6	$41.73	3.136%	$43.0387	$43.04	$43.05	$43.00
Purchase #7	$242.83	13.484%	$275.5732	$275.57	$275.55	$275.60
7 purchase totals =	$853.15		$924.6105	$924.61	$924.60	$924.60