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	$80.50	13.402%	$91.2886	$91.29	$91.30	$91.30
Purchase #2	$215.54	5.699%	$227.8236	$227.82	$227.80	$227.80
Purchase #3	$13.81	12.695%	$15.5632	$15.56	$15.55	$15.60
Purchase #4	$55.26	11.484%	$61.6061	$61.61	$61.60	$61.60
Purchase #5	$70.76	8.809%	$76.9932	$76.99	$77.00	$77.00
Purchase #6	$141.78	10.434%	$156.5733	$156.57	$156.55	$156.60
Purchase #7	$138.74	11.761%	$155.0572	$155.06	$155.05	$155.10
7 purchase totals =	$716.39		$784.9052	$784.90	$784.85	$785.00