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 $193.80   7.757%   $208.8331   $208.83   $208.85   $208.80  
  Purchase #2 $105.94   10.768%   $117.3476   $117.35   $117.35   $117.30  
  Purchase #3 $211.72   13.208%   $239.684   $239.68   $239.70   $239.70  
  Purchase #4 $72.53   13.797%   $82.537   $82.54   $82.55   $82.50  
  Purchase #5 $76.89   5.859%   $81.395   $81.40   $81.40   $81.40  
  Purchase #6 $241.86   3.346%   $249.9526   $249.95   $249.95   $250.00  
  Purchase #7 $47.43   13.374%   $53.7733   $53.77   $53.75   $53.80  
  7 purchase totals = $950.17       $1,033.5226   $1,033.52   $1,033.55   $1,033.50