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	$139.82	4.725%	$146.4265	$146.43	$146.45	$146.40
Purchase #2	$64.40	11.871%	$72.0449	$72.04	$72.05	$72.00
Purchase #3	$106.38	9.578%	$116.5691	$116.57	$116.55	$116.60
Purchase #4	$85.93	9.303%	$93.9241	$93.92	$93.90	$93.90
Purchase #5	$133.73	7.461%	$143.7076	$143.71	$143.70	$143.70
Purchase #6	$44.43	8.391%	$48.1581	$48.16	$48.15	$48.20
Purchase #7	$39.96	5.584%	$42.1914	$42.19	$42.20	$42.20
7 purchase totals =	$614.65		$663.0217	$663.02	$663.00	$663.00