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	$79.65	7.198%	$85.3832	$85.38	$85.40	$85.40
Purchase #2	$59.50	8.660%	$64.6527	$64.65	$64.65	$64.70
Purchase #3	$27.77	10.358%	$30.6464	$30.65	$30.65	$30.60
Purchase #4	$196.94	12.432%	$221.4236	$221.42	$221.40	$221.40
Purchase #5	$164.69	4.827%	$172.6396	$172.64	$172.65	$172.60
Purchase #6	$34.97	11.561%	$39.0129	$39.01	$39.00	$39.00
Purchase #7	$178.56	12.156%	$200.2658	$200.27	$200.25	$200.30
7 purchase totals =	$742.08		$814.0242	$814.02	$814.00	$814.00