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 $92.25   6.775%   $98.4999   $98.50   $98.50   $98.50  
  Purchase #2 $134.36   5.243%   $141.4045   $141.40   $141.40   $141.40  
  Purchase #3 $179.63   12.193%   $201.5323   $201.53   $201.55   $201.50  
  Purchase #4 $23.49   9.226%   $25.6572   $25.66   $25.65   $25.70  
  Purchase #5 $37.98   13.303%   $43.0325   $43.03   $43.05   $43.00  
  Purchase #6 $64.86   3.462%   $67.1055   $67.11   $67.10   $67.10  
  Purchase #7 $202.77   11.369%   $225.8229   $225.82   $225.80   $225.80  
  7 purchase totals = $735.34       $803.0548   $803.05   $803.05   $803.00