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	$67.59	5.596%	$71.3723	$71.37	$71.35	$71.40
Purchase #2	$216.52	13.716%	$246.2179	$246.22	$246.20	$246.20
Purchase #3	$18.55	10.429%	$20.4846	$20.48	$20.50	$20.50
Purchase #4	$83.46	7.132%	$89.4124	$89.41	$89.40	$89.40
Purchase #5	$143.81	3.554%	$148.921	$148.92	$148.90	$148.90
Purchase #6	$152.62	11.697%	$170.472	$170.47	$170.45	$170.50
Purchase #7	$169.93	3.115%	$175.2233	$175.22	$175.20	$175.20
7 purchase totals =	$852.48		$922.1035	$922.09	$922.00	$922.10