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 $239.33   7.615%   $257.555   $257.56   $257.55   $257.60  
  Purchase #2 $170.33   5.246%   $179.2655   $179.27   $179.25   $179.30  
  Purchase #3 $113.45   11.758%   $126.7895   $126.79   $126.80   $126.80  
  Purchase #4 $157.88   12.401%   $177.4587   $177.46   $177.45   $177.50  
  Purchase #5 $205.88   7.473%   $221.2654   $221.27   $221.25   $221.30  
  Purchase #6 $212.87   11.157%   $236.6199   $236.62   $236.60   $236.60  
  Purchase #7 $58.69   6.633%   $62.5829   $62.58   $62.60   $62.60  
  7 purchase totals = $1,158.43       $1,261.5369   $1,261.55   $1,261.50   $1,261.70