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 $82.98   11.182%   $92.2588   $92.26   $92.25   $92.30  
  Purchase #2 $234.44   6.724%   $250.2037   $250.20   $250.20   $250.20  
  Purchase #3 $230.66   4.511%   $241.0651   $241.07   $241.05   $241.10  
  Purchase #4 $58.64   5.577%   $61.9104   $61.91   $61.90   $61.90  
  Purchase #5 $86.72   12.476%   $97.5392   $97.54   $97.55   $97.50  
  Purchase #6 $67.97   9.627%   $74.5135   $74.51   $74.50   $74.50  
  Purchase #7 $99.94   6.870%   $106.8059   $106.81   $106.80   $106.80  
  7 purchase totals = $861.35       $924.2966   $924.30   $924.25   $924.30