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 $96.69   5.501%   $102.0089   $102.01   $102.00   $102.00  
  Purchase #2 $97.43   4.384%   $101.7013   $101.70   $101.70   $101.70  
  Purchase #3 $208.91   7.525%   $224.6305   $224.63   $224.65   $224.60  
  Purchase #4 $216.61   10.789%   $239.9801   $239.98   $240.00   $240.00  
  Purchase #5 $124.81   10.508%   $137.925   $137.93   $137.95   $137.90  
  Purchase #6 $90.26   7.421%   $96.9582   $96.96   $96.95   $97.00  
  Purchase #7 $29.68   5.652%   $31.3575   $31.36   $31.35   $31.40  
  7 purchase totals = $864.39       $934.5615   $934.57   $934.60   $934.60