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	$234.85	6.846%	$250.9278	$250.93	$250.95	$250.90
Purchase #2	$68.45	13.189%	$77.4779	$77.48	$77.50	$77.50
Purchase #3	$212.93	4.376%	$222.2478	$222.25	$222.25	$222.20
Purchase #4	$83.57	9.359%	$91.3913	$91.39	$91.40	$91.40
Purchase #5	$184.85	4.150%	$192.5213	$192.52	$192.50	$192.50
Purchase #6	$96.38	6.739%	$102.875	$102.88	$102.90	$102.90
Purchase #7	$18.73	6.306%	$19.9111	$19.91	$19.90	$19.90
7 purchase totals =	$899.76		$957.3522	$957.36	$957.40	$957.30