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 $53.74   13.458%   $60.9723   $60.97   $60.95   $61.00  
  Purchase #2 $208.25   6.678%   $222.1569   $222.16   $222.15   $222.20  
  Purchase #3 $245.69   5.383%   $258.9155   $258.92   $258.90   $258.90  
  Purchase #4 $37.41   12.375%   $42.0395   $42.04   $42.05   $42.00  
  Purchase #5 $133.36   5.216%   $140.3161   $140.32   $140.30   $140.30  
  Purchase #6 $144.88   13.118%   $163.8854   $163.89   $163.90   $163.90  
  Purchase #7 $98.78   8.433%   $107.1101   $107.11   $107.10   $107.10  
  7 purchase totals = $922.11       $995.3958   $995.41   $995.35   $995.40