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	$238.34	13.503%	$270.5231	$270.52	$270.50	$270.50
Purchase #2	$133.45	8.679%	$145.0321	$145.03	$145.05	$145.00
Purchase #3	$37.55	8.269%	$40.655	$40.66	$40.65	$40.70
Purchase #4	$248.31	13.856%	$282.7158	$282.72	$282.70	$282.70
Purchase #5	$188.67	4.220%	$196.6319	$196.63	$196.65	$196.60
Purchase #6	$103.71	10.463%	$114.5612	$114.56	$114.55	$114.60
Purchase #7	$6.78	12.339%	$7.6166	$7.62	$7.60	$7.60
7 purchase totals =	$956.81		$1,057.7357	$1,057.74	$1,057.70	$1,057.70