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	$131.64	6.742%	$140.5152	$140.52	$140.50	$140.50
Purchase #2	$111.49	6.577%	$118.8227	$118.82	$118.80	$118.80
Purchase #3	$126.49	3.840%	$131.3472	$131.35	$131.35	$131.30
Purchase #4	$131.69	10.455%	$145.4582	$145.46	$145.45	$145.50
Purchase #5	$85.63	7.298%	$91.8793	$91.88	$91.90	$91.90
Purchase #6	$81.89	6.823%	$87.4774	$87.48	$87.50	$87.50
Purchase #7	$131.25	13.489%	$148.9543	$148.95	$148.95	$149.00
7 purchase totals =	$800.08		$864.4543	$864.46	$864.45	$864.50