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 $248.67   6.706%   $265.3458   $265.35   $265.35   $265.30  
  Purchase #2 $211.48   13.145%   $239.279   $239.28   $239.30   $239.30  
  Purchase #3 $67.67   7.203%   $72.5443   $72.54   $72.55   $72.50  
  Purchase #4 $216.85   8.832%   $236.0022   $236.00   $236.00   $236.00  
  Purchase #5 $140.47   8.656%   $152.6291   $152.63   $152.65   $152.60  
  Purchase #6 $107.28   4.355%   $111.952   $111.95   $111.95   $112.00  
  Purchase #7 $228.59   8.683%   $248.4385   $248.44   $248.45   $248.40  
  7 purchase totals = $1,221.01       $1,326.1909   $1,326.19   $1,326.25   $1,326.10