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	$30.48	10.539%	$33.6923	$33.69	$33.70	$33.70
Purchase #2	$196.78	8.378%	$213.2662	$213.27	$213.25	$213.30
Purchase #3	$153.93	12.682%	$173.4514	$173.45	$173.45	$173.50
Purchase #4	$114.36	8.443%	$124.0154	$124.02	$124.00	$124.00
Purchase #5	$85.97	3.698%	$89.1492	$89.15	$89.15	$89.10
Purchase #6	$143.90	10.153%	$158.5102	$158.51	$158.50	$158.50
Purchase #7	$233.61	5.327%	$246.0544	$246.05	$246.05	$246.10
7 purchase totals =	$959.03		$1,038.1391	$1,038.14	$1,038.10	$1,038.20