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 $88.67   4.552%   $92.7063   $92.71   $92.70   $92.70  
  Purchase #2 $26.87   3.335%   $27.7661   $27.77   $27.75   $27.80  
  Purchase #3 $186.89   10.257%   $206.0593   $206.06   $206.05   $206.10  
  Purchase #4 $86.28   4.594%   $90.2437   $90.24   $90.25   $90.20  
  Purchase #5 $14.77   11.691%   $16.4968   $16.50   $16.50   $16.50  
  Purchase #6 $42.67   4.352%   $44.527   $44.53   $44.55   $44.50  
  Purchase #7 $176.97   12.243%   $198.6364   $198.64   $198.65   $198.60  
  7 purchase totals = $623.12       $676.4356   $676.45   $676.45   $676.40