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 $236.68   12.317%   $265.8319   $265.83   $265.85   $265.80  
  Purchase #2 $55.99   3.108%   $57.7302   $57.73   $57.75   $57.70  
  Purchase #3 $131.74   4.649%   $137.8646   $137.86   $137.85   $137.90  
  Purchase #4 $89.87   11.833%   $100.5043   $100.50   $100.50   $100.50  
  Purchase #5 $203.78   6.317%   $216.6528   $216.65   $216.65   $216.70  
  Purchase #6 $53.59   9.830%   $58.8579   $58.86   $58.85   $58.90  
  Purchase #7 $21.87   6.374%   $23.264   $23.26   $23.25   $23.30  
  7 purchase totals = $793.52       $860.7057   $860.69   $860.70   $860.80