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 $229.95   13.717%   $261.4922   $261.49   $261.50   $261.50  
  Purchase #2 $184.31   8.641%   $200.2362   $200.24   $200.25   $200.20  
  Purchase #3 $180.34   3.316%   $186.3201   $186.32   $186.30   $186.30  
  Purchase #4 $167.99   13.834%   $191.2297   $191.23   $191.25   $191.20  
  Purchase #5 $240.91   4.167%   $250.9487   $250.95   $250.95   $250.90  
  Purchase #6 $192.33   6.690%   $205.1969   $205.20   $205.20   $205.20  
  Purchase #7 $146.47   12.792%   $165.2064   $165.21   $165.20   $165.20  
  7 purchase totals = $1,342.30       $1,460.6302   $1,460.64   $1,460.65   $1,460.50