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 $176.32   8.453%   $191.2243   $191.22   $191.20   $191.20  
  Purchase #2 $58.93   11.500%   $65.707   $65.71   $65.70   $65.70  
  Purchase #3 $157.99   12.234%   $177.3185   $177.32   $177.30   $177.30  
  Purchase #4 $240.76   13.794%   $273.9704   $273.97   $273.95   $274.00  
  Purchase #5 $87.62   3.389%   $90.5894   $90.59   $90.60   $90.60  
  Purchase #6 $203.27   6.261%   $215.9967   $216.00   $216.00   $216.00  
  Purchase #7 $14.26   8.271%   $15.4394   $15.44   $15.45   $15.40  
  7 purchase totals = $939.15       $1,030.2457   $1,030.25   $1,030.20   $1,030.20