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 $241.72   6.220%   $256.755   $256.76   $256.75   $256.80  
  Purchase #2 $60.41   9.661%   $66.2462   $66.25   $66.25   $66.20  
  Purchase #3 $223.98   11.365%   $249.4353   $249.44   $249.45   $249.40  
  Purchase #4 $209.42   5.610%   $221.1685   $221.17   $221.15   $221.20  
  Purchase #5 $179.45   12.392%   $201.6874   $201.69   $201.70   $201.70  
  Purchase #6 $21.91   3.140%   $22.598   $22.60   $22.60   $22.60  
  Purchase #7 $25.63   4.458%   $26.7726   $26.77   $26.75   $26.80  
  7 purchase totals = $962.52       $1,044.6630   $1,044.68   $1,044.65   $1,044.70