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	$78.37	12.378%	$88.0706	$88.07	$88.05	$88.10
Purchase #2	$127.30	3.280%	$131.4754	$131.48	$131.50	$131.50
Purchase #3	$167.63	13.610%	$190.4444	$190.44	$190.45	$190.40
Purchase #4	$103.97	9.836%	$114.1965	$114.20	$114.20	$114.20
Purchase #5	$97.49	3.521%	$100.9226	$100.92	$100.90	$100.90
Purchase #6	$190.25	3.316%	$196.5587	$196.56	$196.55	$196.60
Purchase #7	$198.57	9.852%	$218.1331	$218.13	$218.15	$218.10
7 purchase totals =	$963.58		$1,039.8013	$1,039.80	$1,039.80	$1,039.80