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 $57.63   13.448%   $65.3801   $65.38   $65.40   $65.40  
  Purchase #2 $235.80   7.642%   $253.8198   $253.82   $253.80   $253.80  
  Purchase #3 $212.37   11.151%   $236.0514   $236.05   $236.05   $236.10  
  Purchase #4 $117.86   7.593%   $126.8091   $126.81   $126.80   $126.80  
  Purchase #5 $159.76   3.256%   $164.9618   $164.96   $164.95   $165.00  
  Purchase #6 $231.77   11.718%   $258.9288   $258.93   $258.95   $258.90  
  Purchase #7 $15.86   11.709%   $17.717   $17.72   $17.70   $17.70  
  7 purchase totals = $1,031.05       $1,123.6680   $1,123.67   $1,123.65   $1,123.70