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 $234.91   7.721%   $253.0474   $253.05   $253.05   $253.00  
  Purchase #2 $225.48   4.407%   $235.4169   $235.42   $235.40   $235.40  
  Purchase #3 $171.35   4.616%   $179.2595   $179.26   $179.25   $179.30  
  Purchase #4 $170.62   3.507%   $176.6036   $176.60   $176.60   $176.60  
  Purchase #5 $90.92   8.541%   $98.6855   $98.69   $98.70   $98.70  
  Purchase #6 $87.72   6.522%   $93.4411   $93.44   $93.45   $93.40  
  Purchase #7 $6.68   8.720%   $7.2625   $7.26   $7.25   $7.30  
  7 purchase totals = $987.68       $1,043.7165   $1,043.72   $1,043.70   $1,043.70