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	$18.34	12.119%	$20.5626	$20.56	$20.55	$20.60
Purchase #2	$101.86	12.204%	$114.291	$114.29	$114.30	$114.30
Purchase #3	$129.83	7.849%	$140.0204	$140.02	$140.00	$140.00
Purchase #4	$41.50	3.684%	$43.0289	$43.03	$43.05	$43.00
Purchase #5	$102.30	3.582%	$105.9644	$105.96	$105.95	$106.00
Purchase #6	$146.41	6.182%	$155.4611	$155.46	$155.45	$155.50
Purchase #7	$97.85	10.854%	$108.4706	$108.47	$108.45	$108.50
7 purchase totals =	$638.09		$687.7990	$687.79	$687.75	$687.90