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 $240.86   8.569%   $261.4993   $261.50   $261.50   $261.50  
  Purchase #2 $24.29   11.573%   $27.1011   $27.10   $27.10   $27.10  
  Purchase #3 $139.86   8.668%   $151.9831   $151.98   $152.00   $152.00  
  Purchase #4 $183.61   4.567%   $191.9955   $192.00   $192.00   $192.00  
  Purchase #5 $17.90   9.259%   $19.5574   $19.56   $19.55   $19.60  
  Purchase #6 $73.97   12.579%   $83.2747   $83.27   $83.25   $83.30  
  Purchase #7 $45.60   9.281%   $49.8321   $49.83   $49.85   $49.80  
  7 purchase totals = $726.09       $785.2432   $785.24   $785.25   $785.30