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	$206.54	12.272%	$231.8866	$231.89	$231.90	$231.90
Purchase #2	$13.73	3.221%	$14.1722	$14.17	$14.15	$14.20
Purchase #3	$36.94	9.701%	$40.5235	$40.52	$40.50	$40.50
Purchase #4	$83.41	5.397%	$87.9116	$87.91	$87.90	$87.90
Purchase #5	$15.49	11.771%	$17.3133	$17.31	$17.30	$17.30
Purchase #6	$136.59	3.474%	$141.3351	$141.34	$141.35	$141.30
Purchase #7	$78.58	11.204%	$87.3841	$87.38	$87.40	$87.40
7 purchase totals =	$571.28		$620.5264	$620.52	$620.50	$620.50