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 $41.69   9.408%   $45.6122   $45.61   $45.60   $45.60  
  Purchase #2 $61.54   11.365%   $68.534   $68.53   $68.55   $68.50  
  Purchase #3 $124.58   8.215%   $134.8142   $134.81   $134.80   $134.80  
  Purchase #4 $178.84   12.779%   $201.694   $201.69   $201.70   $201.70  
  Purchase #5 $229.95   9.389%   $251.54   $251.54   $251.55   $251.50  
  Purchase #6 $188.56   11.702%   $210.6253   $210.63   $210.65   $210.60  
  Purchase #7 $39.85   10.146%   $43.8932   $43.89   $43.90   $43.90  
  7 purchase totals = $865.01       $956.7129   $956.70   $956.75   $956.60