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 $223.66   11.775%   $249.996   $250.00   $250.00   $250.00  
  Purchase #2 $81.26   8.538%   $88.198   $88.20   $88.20   $88.20  
  Purchase #3 $203.45   12.755%   $229.4   $229.40   $229.40   $229.40  
  Purchase #4 $174.54   5.863%   $184.7733   $184.77   $184.75   $184.80  
  Purchase #5 $160.83   11.546%   $179.3994   $179.40   $179.40   $179.40  
  Purchase #6 $64.91   4.706%   $67.9647   $67.96   $67.95   $68.00  
  Purchase #7 $101.83   6.286%   $108.231   $108.23   $108.25   $108.20  
  7 purchase totals = $1,010.48       $1,107.9624   $1,107.96   $1,107.95   $1,108.00