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 $246.53   8.652%   $267.8598   $267.86   $267.85   $267.90  
  Purchase #2 $62.96   3.509%   $65.1693   $65.17   $65.15   $65.20  
  Purchase #3 $68.70   10.645%   $76.0131   $76.01   $76.00   $76.00  
  Purchase #4 $237.43   12.733%   $267.662   $267.66   $267.65   $267.70  
  Purchase #5 $234.39   10.535%   $259.083   $259.08   $259.10   $259.10  
  Purchase #6 $7.61   3.708%   $7.8922   $7.89   $7.90   $7.90  
  Purchase #7 $170.60   13.424%   $193.5013   $193.50   $193.50   $193.50  
  7 purchase totals = $1,028.22       $1,137.1807   $1,137.17   $1,137.15   $1,137.30