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	$93.31	8.126%	$100.8924	$100.89	$100.90	$100.90
Purchase #2	$200.82	4.795%	$210.4493	$210.45	$210.45	$210.40
Purchase #3	$216.67	5.175%	$227.8827	$227.88	$227.90	$227.90
Purchase #4	$36.25	4.567%	$37.9055	$37.91	$37.90	$37.90
Purchase #5	$138.82	4.316%	$144.8115	$144.81	$144.80	$144.80
Purchase #6	$80.98	12.229%	$90.883	$90.88	$90.90	$90.90
Purchase #7	$28.85	11.320%	$32.1158	$32.12	$32.10	$32.10
7 purchase totals =	$795.70		$844.9402	$844.94	$844.95	$844.90