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 $108.86   9.696%   $119.4151   $119.42   $119.40   $119.40  
  Purchase #2 $246.41   13.128%   $278.7587   $278.76   $278.75   $278.80  
  Purchase #3 $224.54   13.521%   $254.9001   $254.90   $254.90   $254.90  
  Purchase #4 $241.65   9.523%   $264.6623   $264.66   $264.65   $264.70  
  Purchase #5 $49.79   3.604%   $51.5844   $51.58   $51.60   $51.60  
  Purchase #6 $60.40   13.572%   $68.5975   $68.60   $68.60   $68.60  
  Purchase #7 $198.44   8.242%   $214.7954   $214.80   $214.80   $214.80  
  7 purchase totals = $1,130.09       $1,252.7135   $1,252.72   $1,252.70   $1,252.80