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 $183.93   7.110%   $197.0074   $197.01   $197.00   $197.00  
  Purchase #2 $228.62   3.537%   $236.7063   $236.71   $236.70   $236.70  
  Purchase #3 $169.44   5.454%   $178.6813   $178.68   $178.70   $178.70  
  Purchase #4 $67.76   12.592%   $76.2923   $76.29   $76.30   $76.30  
  Purchase #5 $6.58   6.724%   $7.0224   $7.02   $7.00   $7.00  
  Purchase #6 $29.83   3.383%   $30.8391   $30.84   $30.85   $30.80  
  Purchase #7 $44.28   7.784%   $47.7268   $47.73   $47.75   $47.70  
  7 purchase totals = $730.44       $774.2756   $774.28   $774.30   $774.20