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 $207.42   12.529%   $233.4077   $233.41   $233.40   $233.40  
  Purchase #2 $55.57   12.753%   $62.6568   $62.66   $62.65   $62.70  
  Purchase #3 $127.35   7.569%   $136.9891   $136.99   $137.00   $137.00  
  Purchase #4 $45.28   9.787%   $49.7116   $49.71   $49.70   $49.70  
  Purchase #5 $210.91   11.856%   $235.9155   $235.92   $235.90   $235.90  
  Purchase #6 $188.25   11.390%   $209.6917   $209.69   $209.70   $209.70  
  Purchase #7 $55.86   12.536%   $62.8626   $62.86   $62.85   $62.90  
  7 purchase totals = $890.64       $991.2350   $991.24   $991.20   $991.30