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 $23.82   12.198%   $26.7256   $26.73   $26.75   $26.70  
  Purchase #2 $57.29   12.231%   $64.2971   $64.30   $64.30   $64.30  
  Purchase #3 $116.93   5.124%   $122.9215   $122.92   $122.90   $122.90  
  Purchase #4 $24.72   13.616%   $28.0859   $28.09   $28.10   $28.10  
  Purchase #5 $136.98   6.740%   $146.2125   $146.21   $146.20   $146.20  
  Purchase #6 $83.66   8.729%   $90.9627   $90.96   $90.95   $91.00  
  Purchase #7 $217.47   3.277%   $224.5965   $224.60   $224.60   $224.60  
  7 purchase totals = $660.87       $703.8018   $703.81   $703.80   $703.80