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 $110.94   7.414%   $119.1651   $119.17   $119.15   $119.20  
  Purchase #2 $58.38   9.484%   $63.9168   $63.92   $63.90   $63.90  
  Purchase #3 $103.76   13.860%   $118.1411   $118.14   $118.15   $118.10  
  Purchase #4 $246.66   13.276%   $279.4066   $279.41   $279.40   $279.40  
  Purchase #5 $67.54   11.254%   $75.141   $75.14   $75.15   $75.10  
  Purchase #6 $218.31   9.681%   $239.4446   $239.44   $239.45   $239.40  
  Purchase #7 $55.40   9.598%   $60.7173   $60.72   $60.70   $60.70  
  7 purchase totals = $860.99       $955.9325   $955.94   $955.90   $955.80