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	$139.80	7.502%	$150.2878	$150.29	$150.30	$150.30
Purchase #2	$28.61	13.756%	$32.5456	$32.55	$32.55	$32.50
Purchase #3	$61.34	7.627%	$66.0184	$66.02	$66.00	$66.00
Purchase #4	$171.26	12.384%	$192.4688	$192.47	$192.45	$192.50
Purchase #5	$159.54	11.853%	$178.4503	$178.45	$178.45	$178.50
Purchase #6	$37.29	5.553%	$39.3607	$39.36	$39.35	$39.40
Purchase #7	$12.38	7.444%	$13.3016	$13.30	$13.30	$13.30
7 purchase totals =	$610.22		$672.4332	$672.44	$672.40	$672.50