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 $244.49   6.802%   $261.1202   $261.12   $261.10   $261.10  
  Purchase #2 $37.86   10.730%   $41.9224   $41.92   $41.90   $41.90  
  Purchase #3 $41.53   5.293%   $43.7282   $43.73   $43.75   $43.70  
  Purchase #4 $33.43   13.799%   $38.043   $38.04   $38.05   $38.00  
  Purchase #5 $121.40   3.841%   $126.063   $126.06   $126.05   $126.10  
  Purchase #6 $16.35   3.139%   $16.8632   $16.86   $16.85   $16.90  
  Purchase #7 $19.90   12.505%   $22.3885   $22.39   $22.40   $22.40  
  7 purchase totals = $514.96       $550.1285   $550.12   $550.10   $550.10