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	$96.51	13.357%	$109.4008	$109.40	$109.40	$109.40
Purchase #2	$126.93	5.686%	$134.1472	$134.15	$134.15	$134.10
Purchase #3	$134.59	3.262%	$138.9803	$138.98	$139.00	$139.00
Purchase #4	$147.35	13.681%	$167.509	$167.51	$167.50	$167.50
Purchase #5	$66.67	10.585%	$73.727	$73.73	$73.75	$73.70
Purchase #6	$70.50	10.662%	$78.0167	$78.02	$78.00	$78.00
Purchase #7	$149.28	13.157%	$168.9208	$168.92	$168.90	$168.90
7 purchase totals =	$791.83		$870.7018	$870.71	$870.70	$870.60