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 $239.44   10.106%   $263.6378   $263.64   $263.65   $263.60  
  Purchase #2 $38.60   9.804%   $42.3843   $42.38   $42.40   $42.40  
  Purchase #3 $236.63   8.468%   $256.6678   $256.67   $256.65   $256.70  
  Purchase #4 $69.62   3.663%   $72.1702   $72.17   $72.15   $72.20  
  Purchase #5 $165.69   5.712%   $175.1542   $175.15   $175.15   $175.20  
  Purchase #6 $247.59   9.678%   $271.5518   $271.55   $271.55   $271.60  
  Purchase #7 $179.29   4.103%   $186.6463   $186.65   $186.65   $186.60  
  7 purchase totals = $1,176.86       $1,268.2124   $1,268.21   $1,268.20   $1,268.30