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	$144.51	13.872%	$164.5564	$164.56	$164.55	$164.60
Purchase #2	$122.54	12.566%	$137.9384	$137.94	$137.95	$137.90
Purchase #3	$154.79	8.787%	$168.3914	$168.39	$168.40	$168.40
Purchase #4	$85.79	10.489%	$94.7885	$94.79	$94.80	$94.80
Purchase #5	$135.52	6.256%	$143.9981	$144.00	$144.00	$144.00
Purchase #6	$111.91	10.622%	$123.7971	$123.80	$123.80	$123.80
Purchase #7	$18.83	13.192%	$21.3141	$21.31	$21.30	$21.30
7 purchase totals =	$773.89		$854.7840	$854.79	$854.80	$854.80