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 $121.74   9.656%   $133.4952   $133.50   $133.50   $133.50  
  Purchase #2 $226.79   8.585%   $246.2599   $246.26   $246.25   $246.30  
  Purchase #3 $191.63   3.501%   $198.339   $198.34   $198.35   $198.30  
  Purchase #4 $53.95   8.399%   $58.4813   $58.48   $58.50   $58.50  
  Purchase #5 $93.76   5.588%   $98.9993   $99.00   $99.00   $99.00  
  Purchase #6 $5.41   9.188%   $5.9071   $5.91   $5.90   $5.90  
  Purchase #7 $23.63   3.491%   $24.4549   $24.45   $24.45   $24.50  
  7 purchase totals = $716.91       $765.9367   $765.94   $765.95   $766.00