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	$248.68	3.273%	$256.8193	$256.82	$256.80	$256.80
Purchase #2	$175.90	8.250%	$190.4118	$190.41	$190.40	$190.40
Purchase #3	$144.83	13.660%	$164.6138	$164.61	$164.60	$164.60
Purchase #4	$196.92	4.402%	$205.5884	$205.59	$205.60	$205.60
Purchase #5	$66.58	9.183%	$72.694	$72.69	$72.70	$72.70
Purchase #6	$80.92	3.681%	$83.8987	$83.90	$83.90	$83.90
Purchase #7	$151.75	5.648%	$160.3208	$160.32	$160.30	$160.30
7 purchase totals =	$1,065.58		$1,134.3468	$1,134.34	$1,134.30	$1,134.30