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	$64.56	3.855%	$67.0488	$67.05	$67.05	$67.00
Purchase #2	$164.80	5.176%	$173.33	$173.33	$173.35	$173.30
Purchase #3	$213.52	8.552%	$231.7802	$231.78	$231.80	$231.80
Purchase #4	$45.44	5.674%	$48.0183	$48.02	$48.00	$48.00
Purchase #5	$124.71	13.421%	$141.4473	$141.45	$141.45	$141.40
Purchase #6	$37.62	13.509%	$42.7021	$42.70	$42.70	$42.70
Purchase #7	$241.88	13.501%	$274.5362	$274.54	$274.55	$274.50
7 purchase totals =	$892.53		$978.8629	$978.87	$978.90	$978.70