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 $58.92   13.459%   $66.85   $66.85   $66.85   $66.90  
  Purchase #2 $56.86   4.752%   $59.562   $59.56   $59.55   $59.60  
  Purchase #3 $146.48   12.139%   $164.2612   $164.26   $164.25   $164.30  
  Purchase #4 $249.44   3.318%   $257.7164   $257.72   $257.70   $257.70  
  Purchase #5 $88.82   3.862%   $92.2502   $92.25   $92.25   $92.30  
  Purchase #6 $121.87   11.450%   $135.8241   $135.82   $135.80   $135.80  
  Purchase #7 $227.96   4.115%   $237.3406   $237.34   $237.35   $237.30  
  7 purchase totals = $950.35       $1,013.8045   $1,013.80   $1,013.75   $1,013.90