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 $248.27   4.526%   $259.5067   $259.51   $259.50   $259.50  
  Purchase #2 $209.87   12.761%   $236.6515   $236.65   $236.65   $236.70  
  Purchase #3 $85.83   10.218%   $94.6001   $94.60   $94.60   $94.60  
  Purchase #4 $222.88   7.629%   $239.8835   $239.88   $239.90   $239.90  
  Purchase #5 $248.86   13.300%   $281.9584   $281.96   $281.95   $282.00  
  Purchase #6 $184.77   7.474%   $198.5797   $198.58   $198.60   $198.60  
  Purchase #7 $175.71   6.318%   $186.8114   $186.81   $186.80   $186.80  
  7 purchase totals = $1,376.19       $1,497.9913   $1,497.99   $1,498.00   $1,498.10