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	$48.31	5.390%	$50.9139	$50.91	$50.90	$50.90
Purchase #2	$157.91	5.317%	$166.3061	$166.31	$166.30	$166.30
Purchase #3	$134.43	4.117%	$139.9645	$139.96	$139.95	$140.00
Purchase #4	$56.81	4.744%	$59.5051	$59.51	$59.50	$59.50
Purchase #5	$175.66	11.385%	$195.6589	$195.66	$195.65	$195.70
Purchase #6	$109.94	3.265%	$113.5295	$113.53	$113.55	$113.50
Purchase #7	$39.43	7.708%	$42.4693	$42.47	$42.45	$42.50
7 purchase totals =	$722.49		$768.3473	$768.35	$768.30	$768.40