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 $222.97   13.724%   $253.5704   $253.57   $253.55   $253.60  
  Purchase #2 $144.90   11.767%   $161.9504   $161.95   $161.95   $162.00  
  Purchase #3 $113.75   11.120%   $126.399   $126.40   $126.40   $126.40  
  Purchase #4 $14.66   8.837%   $15.9555   $15.96   $15.95   $16.00  
  Purchase #5 $201.92   13.318%   $228.8117   $228.81   $228.80   $228.80  
  Purchase #6 $86.41   7.451%   $92.8484   $92.85   $92.85   $92.80  
  Purchase #7 $225.91   3.567%   $233.9682   $233.97   $233.95   $234.00  
  7 purchase totals = $1,010.52       $1,113.5036   $1,113.51   $1,113.45   $1,113.60