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 $246.95   8.640%   $268.2865   $268.29   $268.30   $268.30  
  Purchase #2 $184.85   4.541%   $193.244   $193.24   $193.25   $193.20  
  Purchase #3 $177.91   4.694%   $186.2611   $186.26   $186.25   $186.30  
  Purchase #4 $236.56   12.207%   $265.4369   $265.44   $265.45   $265.40  
  Purchase #5 $40.38   5.164%   $42.4652   $42.47   $42.45   $42.50  
  Purchase #6 $118.87   10.691%   $131.5784   $131.58   $131.60   $131.60  
  Purchase #7 $156.31   12.573%   $175.9629   $175.96   $175.95   $176.00  
  7 purchase totals = $1,161.83       $1,263.2350   $1,263.24   $1,263.25   $1,263.30