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 $180.32   12.578%   $203.0006   $203.00   $203.00   $203.00  
  Purchase #2 $114.82   4.537%   $120.0294   $120.03   $120.05   $120.00  
  Purchase #3 $76.65   7.836%   $82.6563   $82.66   $82.65   $82.70  
  Purchase #4 $54.98   11.177%   $61.1251   $61.13   $61.15   $61.10  
  Purchase #5 $157.33   9.388%   $172.1001   $172.10   $172.10   $172.10  
  Purchase #6 $233.79   10.788%   $259.0113   $259.01   $259.00   $259.00  
  Purchase #7 $240.92   8.595%   $261.6271   $261.63   $261.65   $261.60  
  7 purchase totals = $1,058.81       $1,159.5499   $1,159.56   $1,159.60   $1,159.50