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	$33.41	3.575%	$34.6044	$34.60	$34.60	$34.60
Purchase #2	$54.53	8.680%	$59.2632	$59.26	$59.25	$59.30
Purchase #3	$186.66	12.874%	$210.6906	$210.69	$210.70	$210.70
Purchase #4	$98.88	6.132%	$104.9433	$104.94	$104.95	$104.90
Purchase #5	$122.41	12.874%	$138.1691	$138.17	$138.15	$138.20
Purchase #6	$78.62	6.365%	$83.6242	$83.62	$83.60	$83.60
Purchase #7	$215.34	3.863%	$223.6586	$223.66	$223.65	$223.70
7 purchase totals =	$789.85		$854.9534	$854.94	$854.90	$855.00