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	$60.34	6.872%	$64.4866	$64.49	$64.50	$64.50
Purchase #2	$106.43	12.259%	$119.4773	$119.48	$119.50	$119.50
Purchase #3	$206.71	6.516%	$220.1792	$220.18	$220.20	$220.20
Purchase #4	$139.78	13.670%	$158.8879	$158.89	$158.90	$158.90
Purchase #5	$229.82	11.719%	$256.7526	$256.75	$256.75	$256.80
Purchase #6	$142.85	7.738%	$153.9037	$153.90	$153.90	$153.90
Purchase #7	$157.60	6.681%	$168.1293	$168.13	$168.15	$168.10
7 purchase totals =	$1,043.53		$1,141.8166	$1,141.82	$1,141.90	$1,141.90