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 $57.31   11.366%   $63.8239   $63.82   $63.80   $63.80  
  Purchase #2 $206.96   13.145%   $234.1649   $234.16   $234.15   $234.20  
  Purchase #3 $126.82   13.320%   $143.7124   $143.71   $143.70   $143.70  
  Purchase #4 $146.80   10.508%   $162.2257   $162.23   $162.25   $162.20  
  Purchase #5 $30.27   8.809%   $32.9365   $32.94   $32.95   $32.90  
  Purchase #6 $153.55   13.453%   $174.2071   $174.21   $174.20   $174.20  
  Purchase #7 $37.88   11.289%   $42.1563   $42.16   $42.15   $42.20  
  7 purchase totals = $759.59       $853.2268   $853.23   $853.20   $853.20