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 $243.27   7.373%   $261.2063   $261.21   $261.20   $261.20  
  Purchase #2 $119.40   4.406%   $124.6608   $124.66   $124.65   $124.70  
  Purchase #3 $211.69   6.749%   $225.977   $225.98   $226.00   $226.00  
  Purchase #4 $22.78   10.445%   $25.1594   $25.16   $25.15   $25.20  
  Purchase #5 $56.95   6.224%   $60.4946   $60.49   $60.50   $60.50  
  Purchase #6 $16.78   13.471%   $19.0404   $19.04   $19.05   $19.00  
  Purchase #7 $178.79   5.523%   $188.6646   $188.66   $188.65   $188.70  
  7 purchase totals = $849.66       $905.2031   $905.20   $905.20   $905.30