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 $95.34   7.766%   $102.7441   $102.74   $102.75   $102.70  
  Purchase #2 $223.93   5.170%   $235.5072   $235.51   $235.50   $235.50  
  Purchase #3 $179.61   9.157%   $196.0569   $196.06   $196.05   $196.10  
  Purchase #4 $209.32   3.605%   $216.866   $216.87   $216.85   $216.90  
  Purchase #5 $50.65   8.788%   $55.1011   $55.10   $55.10   $55.10  
  Purchase #6 $131.50   5.286%   $138.4511   $138.45   $138.45   $138.50  
  Purchase #7 $104.31   9.765%   $114.4959   $114.50   $114.50   $114.50  
  7 purchase totals = $994.66       $1,059.2223   $1,059.23   $1,059.20   $1,059.30