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	$165.85	3.641%	$171.8886	$171.89	$171.90	$171.90
Purchase #2	$82.83	13.299%	$93.8456	$93.85	$93.85	$93.80
Purchase #3	$119.26	11.474%	$132.9439	$132.94	$132.95	$132.90
Purchase #4	$100.35	11.391%	$111.7809	$111.78	$111.80	$111.80
Purchase #5	$103.51	12.286%	$116.2272	$116.23	$116.25	$116.20
Purchase #6	$110.52	11.223%	$122.9237	$122.92	$122.90	$122.90
Purchase #7	$146.48	4.785%	$153.4891	$153.49	$153.50	$153.50
7 purchase totals =	$828.80		$903.0990	$903.10	$903.15	$903.00