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 $208.35   13.239%   $235.9335   $235.93   $235.95   $235.90  
  Purchase #2 $30.47   5.764%   $32.2263   $32.23   $32.25   $32.20  
  Purchase #3 $99.64   4.420%   $104.0441   $104.04   $104.05   $104.00  
  Purchase #4 $108.33   6.809%   $115.7062   $115.71   $115.70   $115.70  
  Purchase #5 $217.77   12.527%   $245.05   $245.05   $245.05   $245.10  
  Purchase #6 $51.46   8.448%   $55.8073   $55.81   $55.80   $55.80  
  Purchase #7 $17.98   4.336%   $18.7596   $18.76   $18.75   $18.80  
  7 purchase totals = $734.00       $807.5270   $807.53   $807.55   $807.50