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 $83.91   10.770%   $92.9471   $92.95   $92.95   $92.90  
  Purchase #2 $119.96   13.209%   $135.8055   $135.81   $135.80   $135.80  
  Purchase #3 $44.39   5.605%   $46.8781   $46.88   $46.90   $46.90  
  Purchase #4 $119.47   9.634%   $130.9797   $130.98   $131.00   $131.00  
  Purchase #5 $208.90   12.288%   $234.5696   $234.57   $234.55   $234.60  
  Purchase #6 $227.28   8.689%   $247.0284   $247.03   $247.05   $247.00  
  Purchase #7 $78.39   6.860%   $83.7676   $83.77   $83.75   $83.80  
  7 purchase totals = $882.30       $971.9760   $971.99   $972.00   $972.00