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 $51.55   11.209%   $57.3282   $57.33   $57.35   $57.30  
  Purchase #2 $171.28   11.122%   $190.3298   $190.33   $190.35   $190.30  
  Purchase #3 $213.57   10.644%   $236.3024   $236.30   $236.30   $236.30  
  Purchase #4 $63.86   9.671%   $70.0359   $70.04   $70.05   $70.00  
  Purchase #5 $207.79   12.576%   $233.9217   $233.92   $233.90   $233.90  
  Purchase #6 $58.54   10.554%   $64.7183   $64.72   $64.70   $64.70  
  Purchase #7 $247.99   5.483%   $261.5873   $261.59   $261.60   $261.60  
  7 purchase totals = $1,014.58       $1,114.2236   $1,114.23   $1,114.25   $1,114.10