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	$85.36	6.490%	$90.8999	$90.90	$90.90	$90.90
Purchase #2	$116.96	10.677%	$129.4478	$129.45	$129.45	$129.40
Purchase #3	$246.63	13.726%	$280.4824	$280.48	$280.50	$280.50
Purchase #4	$187.50	6.846%	$200.3363	$200.34	$200.35	$200.30
Purchase #5	$24.69	10.863%	$27.3721	$27.37	$27.35	$27.40
Purchase #6	$244.95	8.702%	$266.2655	$266.27	$266.25	$266.30
Purchase #7	$189.81	12.600%	$213.7261	$213.73	$213.75	$213.70
7 purchase totals =	$1,095.90		$1,208.5301	$1,208.54	$1,208.55	$1,208.50