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 $44.81   3.849%   $46.5347   $46.53   $46.55   $46.50  
  Purchase #2 $76.28   8.463%   $82.7356   $82.74   $82.75   $82.70  
  Purchase #3 $229.73   12.803%   $259.1423   $259.14   $259.15   $259.10  
  Purchase #4 $91.45   12.308%   $102.7057   $102.71   $102.70   $102.70  
  Purchase #5 $197.74   10.773%   $219.0425   $219.04   $219.05   $219.00  
  Purchase #6 $127.95   9.166%   $139.6779   $139.68   $139.70   $139.70  
  Purchase #7 $86.93   8.681%   $94.4764   $94.48   $94.50   $94.50  
  7 purchase totals = $854.89       $944.3151   $944.32   $944.40   $944.20