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 $210.51   9.541%   $230.5948   $230.59   $230.60   $230.60  
  Purchase #2 $182.88   3.143%   $188.6279   $188.63   $188.65   $188.60  
  Purchase #3 $22.25   13.312%   $25.2119   $25.21   $25.20   $25.20  
  Purchase #4 $185.87   8.545%   $201.7526   $201.75   $201.75   $201.80  
  Purchase #5 $146.63   6.790%   $156.5862   $156.59   $156.60   $156.60  
  Purchase #6 $130.25   3.161%   $134.3672   $134.37   $134.35   $134.40  
  Purchase #7 $131.73   5.137%   $138.497   $138.50   $138.50   $138.50  
  7 purchase totals = $1,010.12       $1,075.6376   $1,075.64   $1,075.65   $1,075.70