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 $106.44   12.391%   $119.629   $119.63   $119.65   $119.60  
  Purchase #2 $16.39   10.721%   $18.1472   $18.15   $18.15   $18.10  
  Purchase #3 $175.46   12.200%   $196.8661   $196.87   $196.85   $196.90  
  Purchase #4 $202.95   12.496%   $228.3106   $228.31   $228.30   $228.30  
  Purchase #5 $136.31   9.803%   $149.6725   $149.67   $149.65   $149.70  
  Purchase #6 $248.30   5.599%   $262.2023   $262.20   $262.20   $262.20  
  Purchase #7 $21.54   3.266%   $22.2435   $22.24   $22.25   $22.20  
  7 purchase totals = $907.39       $997.0712   $997.07   $997.05   $997.00