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 $29.65   13.802%   $33.7423   $33.74   $33.75   $33.70  
  Purchase #2 $148.89   11.267%   $165.6654   $165.67   $165.65   $165.70  
  Purchase #3 $199.74   13.394%   $226.4932   $226.49   $226.50   $226.50  
  Purchase #4 $234.25   8.730%   $254.7   $254.70   $254.70   $254.70  
  Purchase #5 $235.75   4.572%   $246.5285   $246.53   $246.55   $246.50  
  Purchase #6 $51.60   10.376%   $56.954   $56.95   $56.95   $57.00  
  Purchase #7 $158.66   3.703%   $164.5352   $164.54   $164.55   $164.50  
  7 purchase totals = $1,058.54       $1,148.6186   $1,148.62   $1,148.65   $1,148.60