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	$35.94	12.525%	$40.4415	$40.44	$40.45	$40.40
Purchase #2	$73.35	10.369%	$80.9557	$80.96	$80.95	$81.00
Purchase #3	$210.57	13.269%	$238.5105	$238.51	$238.50	$238.50
Purchase #4	$50.46	9.759%	$55.3844	$55.38	$55.40	$55.40
Purchase #5	$244.50	12.362%	$274.7251	$274.73	$274.75	$274.70
Purchase #6	$162.91	5.776%	$172.3197	$172.32	$172.30	$172.30
Purchase #7	$98.44	8.812%	$107.1145	$107.11	$107.10	$107.10
7 purchase totals =	$876.17		$969.4514	$969.45	$969.45	$969.40