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	$103.89	13.371%	$117.7811	$117.78	$117.80	$117.80
Purchase #2	$44.44	4.656%	$46.5091	$46.51	$46.50	$46.50
Purchase #3	$109.84	4.527%	$114.8125	$114.81	$114.80	$114.80
Purchase #4	$57.49	9.531%	$62.9694	$62.97	$62.95	$63.00
Purchase #5	$75.25	10.158%	$82.8939	$82.89	$82.90	$82.90
Purchase #6	$79.83	7.669%	$85.9522	$85.95	$85.95	$86.00
Purchase #7	$183.46	11.700%	$204.9248	$204.92	$204.90	$204.90
7 purchase totals =	$654.20		$715.8430	$715.83	$715.80	$715.90