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	$12.71	9.353%	$13.8988	$13.90	$13.90	$13.90
Purchase #2	$158.76	12.345%	$178.3589	$178.36	$178.35	$178.40
Purchase #3	$231.94	10.709%	$256.7785	$256.78	$256.80	$256.80
Purchase #4	$100.96	4.807%	$105.8131	$105.81	$105.80	$105.80
Purchase #5	$63.92	4.153%	$66.5746	$66.57	$66.55	$66.60
Purchase #6	$215.44	3.281%	$222.5086	$222.51	$222.50	$222.50
Purchase #7	$35.55	4.672%	$37.2109	$37.21	$37.20	$37.20
7 purchase totals =	$819.28		$881.1434	$881.14	$881.10	$881.20