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 $57.58   5.231%   $60.592   $60.59   $60.60   $60.60  
  Purchase #2 $229.44   12.435%   $257.9709   $257.97   $257.95   $258.00  
  Purchase #3 $9.54   6.274%   $10.1385   $10.14   $10.15   $10.10  
  Purchase #4 $217.65   12.241%   $244.2925   $244.29   $244.30   $244.30  
  Purchase #5 $89.41   13.564%   $101.5376   $101.54   $101.55   $101.50  
  Purchase #6 $83.91   9.713%   $92.0602   $92.06   $92.05   $92.10  
  Purchase #7 $122.74   6.762%   $131.0397   $131.04   $131.05   $131.00  
  7 purchase totals = $810.27       $897.6314   $897.63   $897.65   $897.60