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 $239.65   10.681%   $265.247   $265.25   $265.25   $265.20  
  Purchase #2 $106.64   6.377%   $113.4404   $113.44   $113.45   $113.40  
  Purchase #3 $188.57   7.848%   $203.369   $203.37   $203.35   $203.40  
  Purchase #4 $121.88   7.216%   $130.6749   $130.67   $130.65   $130.70  
  Purchase #5 $159.65   12.843%   $180.1538   $180.15   $180.15   $180.20  
  Purchase #6 $245.90   6.392%   $261.6179   $261.62   $261.60   $261.60  
  Purchase #7 $184.41   13.361%   $209.049   $209.05   $209.05   $209.00  
  7 purchase totals = $1,246.70       $1,363.5520   $1,363.55   $1,363.50   $1,363.50