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	$13.47	3.502%	$13.9417	$13.94	$13.95	$13.90
Purchase #2	$184.46	13.767%	$209.8546	$209.85	$209.85	$209.90
Purchase #3	$138.88	12.661%	$156.4636	$156.46	$156.45	$156.50
Purchase #4	$72.60	11.516%	$80.9606	$80.96	$80.95	$81.00
Purchase #5	$156.92	4.542%	$164.0473	$164.05	$164.05	$164.00
Purchase #6	$89.45	4.307%	$93.3026	$93.30	$93.30	$93.30
Purchase #7	$138.74	9.544%	$151.9813	$151.98	$152.00	$152.00
7 purchase totals =	$794.52		$870.5517	$870.54	$870.55	$870.60