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 $54.73   12.545%   $61.5959   $61.60   $61.60   $61.60  
  Purchase #2 $61.76   7.441%   $66.3556   $66.36   $66.35   $66.40  
  Purchase #3 $197.25   3.278%   $203.7159   $203.72   $203.70   $203.70  
  Purchase #4 $200.26   4.170%   $208.6108   $208.61   $208.60   $208.60  
  Purchase #5 $63.93   8.383%   $69.2893   $69.29   $69.30   $69.30  
  Purchase #6 $139.62   12.351%   $156.8645   $156.86   $156.85   $156.90  
  Purchase #7 $206.71   4.281%   $215.5593   $215.56   $215.55   $215.60  
  7 purchase totals = $924.26       $981.9913   $982.00   $981.95   $982.10