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	$52.54	13.276%	$59.5152	$59.52	$59.50	$59.50
Purchase #2	$195.30	7.412%	$209.7756	$209.78	$209.80	$209.80
Purchase #3	$25.51	13.482%	$28.9493	$28.95	$28.95	$28.90
Purchase #4	$111.59	12.257%	$125.2676	$125.27	$125.25	$125.30
Purchase #5	$39.94	13.874%	$45.4813	$45.48	$45.50	$45.50
Purchase #6	$8.98	9.420%	$9.8259	$9.83	$9.85	$9.80
Purchase #7	$90.51	12.422%	$101.7532	$101.75	$101.75	$101.80
7 purchase totals =	$524.37		$580.5681	$580.58	$580.60	$580.60