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	$31.61	8.707%	$34.3623	$34.36	$34.35	$34.40
Purchase #2	$18.25	13.105%	$20.6417	$20.64	$20.65	$20.60
Purchase #3	$189.76	10.178%	$209.0738	$209.07	$209.05	$209.10
Purchase #4	$55.60	6.417%	$59.1679	$59.17	$59.15	$59.20
Purchase #5	$250.90	9.349%	$274.3566	$274.36	$274.35	$274.40
Purchase #6	$153.33	4.853%	$160.7711	$160.77	$160.75	$160.80
Purchase #7	$29.35	9.375%	$32.1016	$32.10	$32.10	$32.10
7 purchase totals =	$728.80		$790.4750	$790.47	$790.40	$790.60