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 $194.75   3.667%   $201.8915   $201.89   $201.90   $201.90  
  Purchase #2 $22.56   6.425%   $24.0095   $24.01   $24.00   $24.00  
  Purchase #3 $185.90   13.344%   $210.7065   $210.71   $210.70   $210.70  
  Purchase #4 $157.79   12.423%   $177.3923   $177.39   $177.40   $177.40  
  Purchase #5 $100.90   5.515%   $106.4646   $106.46   $106.45   $106.50  
  Purchase #6 $95.70   8.765%   $104.0881   $104.09   $104.10   $104.10  
  Purchase #7 $136.65   3.557%   $141.5106   $141.51   $141.50   $141.50  
  7 purchase totals = $894.25       $966.0631   $966.06   $966.05   $966.10