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 $234.68   13.176%   $265.6014   $265.60   $265.60   $265.60  
  Purchase #2 $205.37   5.158%   $215.963   $215.96   $215.95   $216.00  
  Purchase #3 $6.70   7.553%   $7.2061   $7.21   $7.20   $7.20  
  Purchase #4 $142.82   7.264%   $153.1944   $153.19   $153.20   $153.20  
  Purchase #5 $228.77   12.725%   $257.881   $257.88   $257.90   $257.90  
  Purchase #6 $82.66   4.276%   $86.1945   $86.19   $86.20   $86.20  
  Purchase #7 $159.92   3.641%   $165.7427   $165.74   $165.75   $165.70  
  7 purchase totals = $1,060.92       $1,151.7831   $1,151.77   $1,151.80   $1,151.80