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	$10.78	5.156%	$11.3358	$11.34	$11.35	$11.30
Purchase #2	$146.45	12.308%	$164.4751	$164.48	$164.50	$164.50
Purchase #3	$51.53	9.696%	$56.5263	$56.53	$56.55	$56.50
Purchase #4	$125.89	10.554%	$139.1764	$139.18	$139.20	$139.20
Purchase #5	$109.56	7.394%	$117.6609	$117.66	$117.65	$117.70
Purchase #6	$99.30	11.421%	$110.6411	$110.64	$110.65	$110.60
Purchase #7	$59.55	4.128%	$62.0082	$62.01	$62.00	$62.00
7 purchase totals =	$603.06		$661.8238	$661.84	$661.90	$661.80