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	$131.63	13.588%	$149.5159	$149.52	$149.50	$149.50
Purchase #2	$216.50	11.851%	$242.1574	$242.16	$242.15	$242.20
Purchase #3	$155.54	7.605%	$167.3688	$167.37	$167.35	$167.40
Purchase #4	$137.36	13.695%	$156.1715	$156.17	$156.15	$156.20
Purchase #5	$52.59	12.858%	$59.352	$59.35	$59.35	$59.40
Purchase #6	$112.51	11.624%	$125.5882	$125.59	$125.60	$125.60
Purchase #7	$81.77	8.810%	$88.9739	$88.97	$88.95	$89.00
7 purchase totals =	$887.90		$989.1277	$989.13	$989.05	$989.30