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 $208.44   6.329%   $221.6322   $221.63   $221.65   $221.60  
  Purchase #2 $102.74   10.588%   $113.6181   $113.62   $113.60   $113.60  
  Purchase #3 $136.34   6.201%   $144.7944   $144.79   $144.80   $144.80  
  Purchase #4 $204.63   13.456%   $232.165   $232.17   $232.15   $232.20  
  Purchase #5 $26.65   10.474%   $29.4413   $29.44   $29.45   $29.40  
  Purchase #6 $14.54   7.817%   $15.6766   $15.68   $15.70   $15.70  
  Purchase #7 $189.29   6.516%   $201.6241   $201.62   $201.60   $201.60  
  7 purchase totals = $882.63       $958.9517   $958.95   $958.95   $958.90