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	$71.67	9.134%	$78.2163	$78.22	$78.20	$78.20
Purchase #2	$63.78	13.175%	$72.183	$72.18	$72.20	$72.20
Purchase #3	$78.64	8.204%	$85.0916	$85.09	$85.10	$85.10
Purchase #4	$38.75	3.115%	$39.9571	$39.96	$39.95	$40.00
Purchase #5	$231.27	12.536%	$260.262	$260.26	$260.25	$260.30
Purchase #6	$169.26	11.621%	$188.9297	$188.93	$188.95	$188.90
Purchase #7	$27.83	11.628%	$31.0661	$31.07	$31.05	$31.10
7 purchase totals =	$681.20		$755.7058	$755.71	$755.70	$755.80