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	$57.33	12.505%	$64.4991	$64.50	$64.50	$64.50
Purchase #2	$150.79	13.580%	$171.2673	$171.27	$171.25	$171.30
Purchase #3	$37.91	13.379%	$42.982	$42.98	$43.00	$43.00
Purchase #4	$49.49	12.465%	$55.6589	$55.66	$55.65	$55.70
Purchase #5	$44.89	8.874%	$48.8735	$48.87	$48.85	$48.90
Purchase #6	$25.54	6.715%	$27.255	$27.26	$27.25	$27.30
Purchase #7	$241.89	3.428%	$250.182	$250.18	$250.20	$250.20
7 purchase totals =	$607.84		$660.7178	$660.72	$660.70	$660.90