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	$40.80	7.359%	$43.8025	$43.80	$43.80	$43.80
Purchase #2	$83.50	8.171%	$90.3228	$90.32	$90.30	$90.30
Purchase #3	$193.70	9.696%	$212.4812	$212.48	$212.50	$212.50
Purchase #4	$42.93	7.756%	$46.2597	$46.26	$46.25	$46.30
Purchase #5	$11.85	6.504%	$12.6207	$12.62	$12.60	$12.60
Purchase #6	$36.73	9.106%	$40.0746	$40.07	$40.05	$40.10
Purchase #7	$235.36	8.690%	$255.8128	$255.81	$255.80	$255.80
7 purchase totals =	$644.87		$701.3743	$701.36	$701.30	$701.40