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 $144.82   13.277%   $164.0478   $164.05   $164.05   $164.00  
  Purchase #2 $58.59   8.811%   $63.7524   $63.75   $63.75   $63.80  
  Purchase #3 $117.61   7.812%   $126.7977   $126.80   $126.80   $126.80  
  Purchase #4 $193.36   10.520%   $213.7015   $213.70   $213.70   $213.70  
  Purchase #5 $75.77   4.329%   $79.0501   $79.05   $79.05   $79.10  
  Purchase #6 $118.97   13.154%   $134.6193   $134.62   $134.60   $134.60  
  Purchase #7 $187.56   8.290%   $203.1087   $203.11   $203.10   $203.10  
  7 purchase totals = $896.68       $985.0775   $985.08   $985.05   $985.10