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 $86.93   8.438%   $94.2652   $94.27   $94.25   $94.30  
  Purchase #2 $164.41   11.768%   $183.7578   $183.76   $183.75   $183.80  
  Purchase #3 $20.29   6.271%   $21.5624   $21.56   $21.55   $21.60  
  Purchase #4 $29.68   13.787%   $33.772   $33.77   $33.75   $33.80  
  Purchase #5 $223.79   9.519%   $245.0926   $245.09   $245.10   $245.10  
  Purchase #6 $157.26   11.684%   $175.6343   $175.63   $175.65   $175.60  
  Purchase #7 $118.71   5.280%   $124.9779   $124.98   $125.00   $125.00  
  7 purchase totals = $801.07       $879.0622   $879.06   $879.05   $879.20