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	$247.55	10.446%	$273.4091	$273.41	$273.40	$273.40
Purchase #2	$21.60	13.578%	$24.5328	$24.53	$24.55	$24.50
Purchase #3	$61.66	8.522%	$66.9147	$66.91	$66.90	$66.90
Purchase #4	$55.61	4.828%	$58.2949	$58.29	$58.30	$58.30
Purchase #5	$102.41	3.421%	$105.9134	$105.91	$105.90	$105.90
Purchase #6	$31.62	7.414%	$33.9643	$33.96	$33.95	$34.00
Purchase #7	$90.27	10.756%	$99.9794	$99.98	$100.00	$100.00
7 purchase totals =	$610.72		$663.0086	$662.99	$663.00	$663.00