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 $78.54   8.139%   $84.9324   $84.93   $84.95   $84.90  
  Purchase #2 $213.26   13.624%   $242.3145   $242.31   $242.30   $242.30  
  Purchase #3 $234.40   5.129%   $246.4224   $246.42   $246.40   $246.40  
  Purchase #4 $37.45   12.404%   $42.0953   $42.10   $42.10   $42.10  
  Purchase #5 $154.42   10.760%   $171.0356   $171.04   $171.05   $171.00  
  Purchase #6 $222.49   10.543%   $245.9471   $245.95   $245.95   $245.90  
  Purchase #7 $207.88   4.811%   $217.8811   $217.88   $217.90   $217.90  
  7 purchase totals = $1,148.44       $1,250.6284   $1,250.63   $1,250.65   $1,250.50