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	$40.46	7.448%	$43.4735	$43.47	$43.45	$43.50
Purchase #2	$129.63	5.864%	$137.2315	$137.23	$137.25	$137.20
Purchase #3	$201.69	13.600%	$229.1198	$229.12	$229.10	$229.10
Purchase #4	$201.31	4.768%	$210.9085	$210.91	$210.90	$210.90
Purchase #5	$117.72	4.745%	$123.3058	$123.31	$123.30	$123.30
Purchase #6	$116.94	13.149%	$132.3164	$132.32	$132.30	$132.30
Purchase #7	$84.95	7.499%	$91.3204	$91.32	$91.30	$91.30
7 purchase totals =	$892.70		$967.6759	$967.68	$967.60	$967.60