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	$82.39	9.547%	$90.2558	$90.26	$90.25	$90.30
Purchase #2	$30.59	5.437%	$32.2532	$32.25	$32.25	$32.30
Purchase #3	$36.98	9.826%	$40.6137	$40.61	$40.60	$40.60
Purchase #4	$239.56	6.645%	$255.4788	$255.48	$255.50	$255.50
Purchase #5	$177.90	8.815%	$193.5819	$193.58	$193.60	$193.60
Purchase #6	$38.86	13.851%	$44.2425	$44.24	$44.25	$44.20
Purchase #7	$31.57	9.758%	$34.6506	$34.65	$34.65	$34.70
7 purchase totals =	$637.85		$691.0765	$691.07	$691.10	$691.20