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 $134.61   5.274%   $141.7093   $141.71   $141.70   $141.70  
  Purchase #2 $210.66   10.519%   $232.8193   $232.82   $232.80   $232.80  
  Purchase #3 $188.39   9.863%   $206.9709   $206.97   $206.95   $207.00  
  Purchase #4 $185.59   8.641%   $201.6268   $201.63   $201.65   $201.60  
  Purchase #5 $17.34   5.430%   $18.2816   $18.28   $18.30   $18.30  
  Purchase #6 $114.90   12.846%   $129.6601   $129.66   $129.65   $129.70  
  Purchase #7 $23.85   3.228%   $24.6199   $24.62   $24.60   $24.60  
  7 purchase totals = $875.34       $955.6879   $955.69   $955.65   $955.70