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 $83.69   3.753%   $86.8309   $86.83   $86.85   $86.80  
  Purchase #2 $94.30   8.167%   $102.0015   $102.00   $102.00   $102.00  
  Purchase #3 $175.65   10.138%   $193.4574   $193.46   $193.45   $193.50  
  Purchase #4 $199.93   13.289%   $226.4987   $226.50   $226.50   $226.50  
  Purchase #5 $218.49   5.838%   $231.2454   $231.25   $231.25   $231.20  
  Purchase #6 $74.79   8.652%   $81.2608   $81.26   $81.25   $81.30  
  Purchase #7 $41.76   3.765%   $43.3323   $43.33   $43.35   $43.30  
  7 purchase totals = $888.61       $964.6270   $964.63   $964.65   $964.60