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 $114.55   3.824%   $118.9304   $118.93   $118.95   $118.90  
  Purchase #2 $242.70   3.272%   $250.6411   $250.64   $250.65   $250.60  
  Purchase #3 $183.47   4.429%   $191.5959   $191.60   $191.60   $191.60  
  Purchase #4 $241.35   6.524%   $257.0957   $257.10   $257.10   $257.10  
  Purchase #5 $250.55   6.469%   $266.7581   $266.76   $266.75   $266.80  
  Purchase #6 $62.55   11.107%   $69.4974   $69.50   $69.50   $69.50  
  Purchase #7 $157.33   9.147%   $171.721   $171.72   $171.70   $171.70  
  7 purchase totals = $1,252.50       $1,326.2396   $1,326.25   $1,326.25   $1,326.20