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 $87.43   6.710%   $93.2966   $93.30   $93.30   $93.30  
  Purchase #2 $182.86   11.387%   $203.6823   $203.68   $203.70   $203.70  
  Purchase #3 $23.36   11.432%   $26.0305   $26.03   $26.05   $26.00  
  Purchase #4 $42.75   11.599%   $47.7086   $47.71   $47.70   $47.70  
  Purchase #5 $113.83   4.516%   $118.9706   $118.97   $118.95   $119.00  
  Purchase #6 $114.97   6.866%   $122.8638   $122.86   $122.85   $122.90  
  Purchase #7 $152.52   8.294%   $165.17   $165.17   $165.15   $165.20  
  7 purchase totals = $717.72       $777.7224   $777.72   $777.70   $777.80