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 $188.26   7.202%   $201.8185   $201.82   $201.80   $201.80  
  Purchase #2 $16.66   11.541%   $18.5827   $18.58   $18.60   $18.60  
  Purchase #3 $68.56   4.327%   $71.5266   $71.53   $71.55   $71.50  
  Purchase #4 $232.87   12.173%   $261.2173   $261.22   $261.20   $261.20  
  Purchase #5 $223.27   12.553%   $251.2971   $251.30   $251.30   $251.30  
  Purchase #6 $20.85   8.524%   $22.6273   $22.63   $22.65   $22.60  
  Purchase #7 $8.61   6.649%   $9.1825   $9.18   $9.20   $9.20  
  7 purchase totals = $759.08       $836.2520   $836.26   $836.30   $836.20