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	$109.82	8.232%	$118.8604	$118.86	$118.85	$118.90
Purchase #2	$180.30	9.607%	$197.6214	$197.62	$197.60	$197.60
Purchase #3	$93.69	10.153%	$103.2023	$103.20	$103.20	$103.20
Purchase #4	$50.64	10.150%	$55.78	$55.78	$55.80	$55.80
Purchase #5	$87.25	12.859%	$98.4695	$98.47	$98.45	$98.50
Purchase #6	$40.33	12.166%	$45.2365	$45.24	$45.25	$45.20
Purchase #7	$150.91	11.515%	$168.2873	$168.29	$168.30	$168.30
7 purchase totals =	$712.94		$787.4574	$787.46	$787.45	$787.50