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 $230.26   13.762%   $261.9484   $261.95   $261.95   $261.90  
  Purchase #2 $82.31   11.839%   $92.0547   $92.05   $92.05   $92.10  
  Purchase #3 $181.48   7.118%   $194.3977   $194.40   $194.40   $194.40  
  Purchase #4 $122.31   3.808%   $126.9676   $126.97   $126.95   $127.00  
  Purchase #5 $188.44   9.838%   $206.9787   $206.98   $207.00   $207.00  
  Purchase #6 $68.69   12.782%   $77.47   $77.47   $77.45   $77.50  
  Purchase #7 $172.86   4.640%   $180.8807   $180.88   $180.90   $180.90  
  7 purchase totals = $1,046.35       $1,140.6978   $1,140.70   $1,140.70   $1,140.80