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 $225.83   11.277%   $251.2968   $251.30   $251.30   $251.30  
  Purchase #2 $161.88   9.115%   $176.6354   $176.64   $176.65   $176.60  
  Purchase #3 $11.37   9.681%   $12.4707   $12.47   $12.45   $12.50  
  Purchase #4 $65.89   10.274%   $72.6595   $72.66   $72.65   $72.70  
  Purchase #5 $104.62   9.748%   $114.8184   $114.82   $114.80   $114.80  
  Purchase #6 $229.70   10.478%   $253.768   $253.77   $253.75   $253.80  
  Purchase #7 $240.76   6.460%   $256.3131   $256.31   $256.30   $256.30  
  7 purchase totals = $1,040.05       $1,137.9619   $1,137.97   $1,137.90   $1,138.00