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 $249.82   6.865%   $266.9701   $266.97   $266.95   $267.00  
  Purchase #2 $37.58   5.726%   $39.7318   $39.73   $39.75   $39.70  
  Purchase #3 $91.95   3.839%   $95.48   $95.48   $95.50   $95.50  
  Purchase #4 $155.53   13.327%   $176.2575   $176.26   $176.25   $176.30  
  Purchase #5 $203.56   5.484%   $214.7232   $214.72   $214.70   $214.70  
  Purchase #6 $37.32   3.860%   $38.7606   $38.76   $38.75   $38.80  
  Purchase #7 $112.29   9.353%   $122.7925   $122.79   $122.80   $122.80  
  7 purchase totals = $888.05       $954.7157   $954.71   $954.70   $954.80