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 $134.92   12.857%   $152.2667   $152.27   $152.25   $152.30  
  Purchase #2 $244.93   11.743%   $273.6921   $273.69   $273.70   $273.70  
  Purchase #3 $209.43   13.593%   $237.8978   $237.90   $237.90   $237.90  
  Purchase #4 $34.63   11.657%   $38.6668   $38.67   $38.65   $38.70  
  Purchase #5 $162.56   12.411%   $182.7353   $182.74   $182.75   $182.70  
  Purchase #6 $14.49   13.153%   $16.3959   $16.40   $16.40   $16.40  
  Purchase #7 $149.31   10.423%   $164.8726   $164.87   $164.85   $164.90  
  7 purchase totals = $950.27       $1,066.5272   $1,066.54   $1,066.50   $1,066.60