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 $234.95   11.489%   $261.9434   $261.94   $261.95   $261.90  
  Purchase #2 $59.31   9.639%   $65.0269   $65.03   $65.05   $65.00  
  Purchase #3 $148.69   13.570%   $168.8672   $168.87   $168.85   $168.90  
  Purchase #4 $65.92   11.323%   $73.3841   $73.38   $73.40   $73.40  
  Purchase #5 $17.99   8.518%   $19.5224   $19.52   $19.50   $19.50  
  Purchase #6 $138.74   10.773%   $153.6865   $153.69   $153.70   $153.70  
  Purchase #7 $33.44   3.134%   $34.488   $34.49   $34.50   $34.50  
  7 purchase totals = $699.04       $776.9185   $776.92   $776.95   $776.90