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	$125.72	7.393%	$135.0145	$135.01	$135.00	$135.00
Purchase #2	$90.59	10.114%	$99.7523	$99.75	$99.75	$99.80
Purchase #3	$242.58	5.741%	$256.5065	$256.51	$256.50	$256.50
Purchase #4	$153.89	9.666%	$168.765	$168.77	$168.75	$168.80
Purchase #5	$150.95	12.671%	$170.0769	$170.08	$170.10	$170.10
Purchase #6	$243.47	7.397%	$261.4795	$261.48	$261.50	$261.50
Purchase #7	$246.65	4.154%	$256.8958	$256.90	$256.90	$256.90
7 purchase totals =	$1,253.85		$1,348.4905	$1,348.50	$1,348.50	$1,348.60