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 $58.89   7.252%   $63.1607   $63.16   $63.15   $63.20  
  Purchase #2 $240.98   4.544%   $251.9301   $251.93   $251.95   $251.90  
  Purchase #3 $6.58   4.676%   $6.8877   $6.89   $6.90   $6.90  
  Purchase #4 $114.54   7.282%   $122.8808   $122.88   $122.90   $122.90  
  Purchase #5 $43.71   8.423%   $47.3917   $47.39   $47.40   $47.40  
  Purchase #6 $139.40   9.396%   $152.498   $152.50   $152.50   $152.50  
  Purchase #7 $200.53   10.578%   $221.7421   $221.74   $221.75   $221.70  
  7 purchase totals = $804.63       $866.4911   $866.49   $866.55   $866.50