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 $245.94   9.403%   $269.0657   $269.07   $269.05   $269.10  
  Purchase #2 $30.98   4.318%   $32.3177   $32.32   $32.30   $32.30  
  Purchase #3 $213.89   11.242%   $237.9355   $237.94   $237.95   $237.90  
  Purchase #4 $163.48   8.231%   $176.936   $176.94   $176.95   $176.90  
  Purchase #5 $177.83   13.274%   $201.4352   $201.44   $201.45   $201.40  
  Purchase #6 $157.40   5.352%   $165.824   $165.82   $165.80   $165.80  
  Purchase #7 $13.67   3.786%   $14.1875   $14.19   $14.20   $14.20  
  7 purchase totals = $1,003.19       $1,097.7016   $1,097.72   $1,097.70   $1,097.60