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	$13.35	12.496%	$15.0182	$15.02	$15.00	$15.00
Purchase #2	$66.50	9.634%	$72.9066	$72.91	$72.90	$72.90
Purchase #3	$27.34	10.357%	$30.1716	$30.17	$30.15	$30.20
Purchase #4	$71.30	13.529%	$80.9462	$80.95	$80.95	$80.90
Purchase #5	$168.32	6.618%	$179.4594	$179.46	$179.45	$179.50
Purchase #6	$164.47	6.563%	$175.2642	$175.26	$175.25	$175.30
Purchase #7	$247.41	9.837%	$271.7477	$271.75	$271.75	$271.70
7 purchase totals =	$758.69		$825.5139	$825.52	$825.45	$825.50