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 $138.77   9.639%   $152.146   $152.15   $152.15   $152.10  
  Purchase #2 $35.69   9.109%   $38.941   $38.94   $38.95   $38.90  
  Purchase #3 $216.75   6.439%   $230.7065   $230.71   $230.70   $230.70  
  Purchase #4 $200.62   8.507%   $217.6867   $217.69   $217.70   $217.70  
  Purchase #5 $229.50   5.196%   $241.4248   $241.42   $241.40   $241.40  
  Purchase #6 $176.71   4.216%   $184.1601   $184.16   $184.15   $184.20  
  Purchase #7 $156.50   9.553%   $171.4504   $171.45   $171.45   $171.50  
  7 purchase totals = $1,154.54       $1,236.5155   $1,236.52   $1,236.50   $1,236.50