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	$164.85	9.588%	$180.6558	$180.66	$180.65	$180.70
Purchase #2	$45.91	8.394%	$49.7637	$49.76	$49.75	$49.80
Purchase #3	$86.38	4.217%	$90.0226	$90.02	$90.00	$90.00
Purchase #4	$80.65	11.412%	$89.8538	$89.85	$89.85	$89.90
Purchase #5	$40.37	6.233%	$42.8863	$42.89	$42.90	$42.90
Purchase #6	$87.84	7.379%	$94.3217	$94.32	$94.30	$94.30
Purchase #7	$60.53	4.645%	$63.3416	$63.34	$63.35	$63.30
7 purchase totals =	$566.53		$610.8455	$610.84	$610.80	$610.90