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	$8.46	5.383%	$8.9154	$8.92	$8.90	$8.90
Purchase #2	$32.34	13.194%	$36.6069	$36.61	$36.60	$36.60
Purchase #3	$211.92	5.448%	$223.4654	$223.47	$223.45	$223.50
Purchase #4	$43.43	5.520%	$45.8273	$45.83	$45.85	$45.80
Purchase #5	$75.66	6.870%	$80.8578	$80.86	$80.85	$80.90
Purchase #6	$26.57	11.840%	$29.7159	$29.72	$29.70	$29.70
Purchase #7	$155.30	10.501%	$171.6081	$171.61	$171.60	$171.60
7 purchase totals =	$553.68		$596.9968	$597.02	$596.95	$597.00