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 $62.66   3.265%   $64.7058   $64.71   $64.70   $64.70  
  Purchase #2 $51.32   11.857%   $57.405   $57.41   $57.40   $57.40  
  Purchase #3 $137.59   5.118%   $144.6319   $144.63   $144.65   $144.60  
  Purchase #4 $61.94   5.266%   $65.2018   $65.20   $65.20   $65.20  
  Purchase #5 $199.76   5.640%   $211.0265   $211.03   $211.05   $211.00  
  Purchase #6 $210.60   12.556%   $237.0429   $237.04   $237.05   $237.00  
  Purchase #7 $250.50   5.581%   $264.4804   $264.48   $264.50   $264.50  
  7 purchase totals = $974.37       $1,044.4943   $1,044.50   $1,044.55   $1,044.40