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	$142.91	11.492%	$159.3332	$159.33	$159.35	$159.30
Purchase #2	$127.57	12.770%	$143.8607	$143.86	$143.85	$143.90
Purchase #3	$208.35	12.617%	$234.6375	$234.64	$234.65	$234.60
Purchase #4	$195.98	7.383%	$210.4492	$210.45	$210.45	$210.40
Purchase #5	$160.32	7.648%	$172.5813	$172.58	$172.60	$172.60
Purchase #6	$157.29	4.651%	$164.6056	$164.61	$164.60	$164.60
Purchase #7	$159.64	6.863%	$170.5961	$170.60	$170.60	$170.60
7 purchase totals =	$1,152.06		$1,256.0636	$1,256.07	$1,256.10	$1,256.00