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 $85.48   10.396%   $94.3665   $94.37   $94.35   $94.40  
  Purchase #2 $224.66   8.648%   $244.0886   $244.09   $244.10   $244.10  
  Purchase #3 $22.32   6.333%   $23.7335   $23.73   $23.75   $23.70  
  Purchase #4 $234.46   9.637%   $257.0549   $257.05   $257.05   $257.10  
  Purchase #5 $24.71   4.702%   $25.8719   $25.87   $25.85   $25.90  
  Purchase #6 $85.88   10.754%   $95.1155   $95.12   $95.10   $95.10  
  Purchase #7 $244.88   4.423%   $255.711   $255.71   $255.70   $255.70  
  7 purchase totals = $922.39       $995.9419   $995.94   $995.90   $996.00