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 $59.93   5.192%   $63.0416   $63.04   $63.05   $63.00  
  Purchase #2 $126.62   13.286%   $143.4427   $143.44   $143.45   $143.40  
  Purchase #3 $92.81   11.724%   $103.691   $103.69   $103.70   $103.70  
  Purchase #4 $35.98   5.454%   $37.9423   $37.94   $37.95   $37.90  
  Purchase #5 $129.50   4.783%   $135.694   $135.69   $135.70   $135.70  
  Purchase #6 $69.53   5.350%   $73.2499   $73.25   $73.25   $73.20  
  Purchase #7 $8.62   5.722%   $9.1132   $9.11   $9.10   $9.10  
  7 purchase totals = $522.99       $566.1747   $566.16   $566.20   $566.00