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 $236.75   10.624%   $261.9023   $261.90   $261.90   $261.90  
  Purchase #2 $146.25   3.460%   $151.3103   $151.31   $151.30   $151.30  
  Purchase #3 $6.92   8.525%   $7.5099   $7.51   $7.50   $7.50  
  Purchase #4 $61.69   8.271%   $66.7924   $66.79   $66.80   $66.80  
  Purchase #5 $71.71   12.265%   $80.5052   $80.51   $80.50   $80.50  
  Purchase #6 $103.41   3.651%   $107.1855   $107.19   $107.20   $107.20  
  Purchase #7 $91.96   3.847%   $95.4977   $95.50   $95.50   $95.50  
  7 purchase totals = $718.69       $770.7033   $770.71   $770.70   $770.70