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 $51.49   12.607%   $57.9813   $57.98   $58.00   $58.00  
  Purchase #2 $107.25   3.272%   $110.7592   $110.76   $110.75   $110.80  
  Purchase #3 $110.86   4.410%   $115.7489   $115.75   $115.75   $115.70  
  Purchase #4 $153.46   5.650%   $162.1305   $162.13   $162.15   $162.10  
  Purchase #5 $237.94   11.656%   $265.6743   $265.67   $265.65   $265.70  
  Purchase #6 $248.83   5.527%   $262.5828   $262.58   $262.60   $262.60  
  Purchase #7 $208.78   8.147%   $225.7893   $225.79   $225.80   $225.80  
  7 purchase totals = $1,118.61       $1,200.6663   $1,200.66   $1,200.70   $1,200.70