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 $76.29   7.682%   $82.1506   $82.15   $82.15   $82.20  
  Purchase #2 $94.68   13.710%   $107.6606   $107.66   $107.65   $107.70  
  Purchase #3 $82.49   12.749%   $93.0067   $93.01   $93.00   $93.00  
  Purchase #4 $131.42   8.346%   $142.3883   $142.39   $142.40   $142.40  
  Purchase #5 $165.77   6.524%   $176.5848   $176.58   $176.60   $176.60  
  Purchase #6 $162.72   8.821%   $177.0735   $177.07   $177.05   $177.10  
  Purchase #7 $146.34   12.250%   $164.2667   $164.27   $164.25   $164.30  
  7 purchase totals = $859.71       $943.1312   $943.13   $943.10   $943.30