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 $246.73   13.726%   $280.5962   $280.60   $280.60   $280.60  
  Purchase #2 $177.28   10.495%   $195.8855   $195.89   $195.90   $195.90  
  Purchase #3 $113.74   3.624%   $117.8619   $117.86   $117.85   $117.90  
  Purchase #4 $163.76   8.363%   $177.4552   $177.46   $177.45   $177.50  
  Purchase #5 $83.44   9.756%   $91.5804   $91.58   $91.60   $91.60  
  Purchase #6 $164.49   12.808%   $185.5579   $185.56   $185.55   $185.60  
  Purchase #7 $10.88   8.586%   $11.8142   $11.81   $11.80   $11.80  
  7 purchase totals = $960.32       $1,060.7513   $1,060.76   $1,060.75   $1,060.90