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 $239.56   13.164%   $271.0957   $271.10   $271.10   $271.10  
  Purchase #2 $44.76   10.826%   $49.6057   $49.61   $49.60   $49.60  
  Purchase #3 $52.99   13.473%   $60.1293   $60.13   $60.15   $60.10  
  Purchase #4 $24.47   11.786%   $27.354   $27.35   $27.35   $27.40  
  Purchase #5 $41.95   5.652%   $44.321   $44.32   $44.30   $44.30  
  Purchase #6 $17.67   4.750%   $18.5093   $18.51   $18.50   $18.50  
  Purchase #7 $213.53   6.280%   $226.9397   $226.94   $226.95   $226.90  
  7 purchase totals = $634.93       $697.9547   $697.96   $697.95   $697.90