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	$87.45	3.140%	$90.1959	$90.20	$90.20	$90.20
Purchase #2	$145.56	7.473%	$156.4377	$156.44	$156.45	$156.40
Purchase #3	$101.99	11.179%	$113.3915	$113.39	$113.40	$113.40
Purchase #4	$238.83	9.510%	$261.5427	$261.54	$261.55	$261.50
Purchase #5	$84.81	4.353%	$88.5018	$88.50	$88.50	$88.50
Purchase #6	$228.46	4.205%	$238.0667	$238.07	$238.05	$238.10
Purchase #7	$222.73	4.323%	$232.3586	$232.36	$232.35	$232.40
7 purchase totals =	$1,109.83		$1,180.4949	$1,180.50	$1,180.50	$1,180.50