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	$52.89	12.265%	$59.377	$59.38	$59.40	$59.40
Purchase #2	$218.69	10.769%	$242.2407	$242.24	$242.25	$242.20
Purchase #3	$102.51	9.760%	$112.515	$112.52	$112.50	$112.50
Purchase #4	$18.87	13.318%	$21.3831	$21.38	$21.40	$21.40
Purchase #5	$85.32	3.755%	$88.5238	$88.52	$88.50	$88.50
Purchase #6	$130.83	12.338%	$146.9718	$146.97	$146.95	$147.00
Purchase #7	$134.45	8.856%	$146.3569	$146.36	$146.35	$146.40
7 purchase totals =	$743.56		$817.3683	$817.37	$817.35	$817.40