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 $150.38   7.817%   $162.1352   $162.14   $162.15   $162.10  
  Purchase #2 $232.48   12.268%   $261.0006   $261.00   $261.00   $261.00  
  Purchase #3 $165.97   9.582%   $181.8732   $181.87   $181.85   $181.90  
  Purchase #4 $48.89   8.239%   $52.918   $52.92   $52.90   $52.90  
  Purchase #5 $13.77   6.123%   $14.6131   $14.61   $14.60   $14.60  
  Purchase #6 $233.83   11.274%   $260.192   $260.19   $260.20   $260.20  
  Purchase #7 $190.85   8.597%   $207.2574   $207.26   $207.25   $207.30  
  7 purchase totals = $1,036.17       $1,139.9895   $1,139.99   $1,139.95   $1,140.00