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	$130.52	5.860%	$138.1685	$138.17	$138.15	$138.20
Purchase #2	$61.74	9.773%	$67.7739	$67.77	$67.75	$67.80
Purchase #3	$32.38	12.156%	$36.3161	$36.32	$36.30	$36.30
Purchase #4	$131.34	7.661%	$141.402	$141.40	$141.40	$141.40
Purchase #5	$84.86	12.322%	$95.3164	$95.32	$95.30	$95.30
Purchase #6	$62.71	6.407%	$66.7278	$66.73	$66.75	$66.70
Purchase #7	$208.27	6.757%	$222.3428	$222.34	$222.35	$222.30
7 purchase totals =	$711.82		$768.0475	$768.05	$768.00	$768.00