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 $53.26   8.769%   $57.9304   $57.93   $57.95   $57.90  
  Purchase #2 $186.99   7.610%   $201.2199   $201.22   $201.20   $201.20  
  Purchase #3 $247.59   3.385%   $255.9709   $255.97   $255.95   $256.00  
  Purchase #4 $134.29   13.484%   $152.3977   $152.40   $152.40   $152.40  
  Purchase #5 $121.30   9.846%   $133.2432   $133.24   $133.25   $133.20  
  Purchase #6 $58.52   6.369%   $62.2471   $62.25   $62.25   $62.20  
  Purchase #7 $47.61   12.626%   $53.6212   $53.62   $53.60   $53.60  
  7 purchase totals = $849.56       $916.6304   $916.63   $916.60   $916.50