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 $120.99   4.503%   $126.4382   $126.44   $126.45   $126.40  
  Purchase #2 $188.62   4.867%   $197.8001   $197.80   $197.80   $197.80  
  Purchase #3 $220.94   5.547%   $233.1955   $233.20   $233.20   $233.20  
  Purchase #4 $82.87   3.545%   $85.8077   $85.81   $85.80   $85.80  
  Purchase #5 $212.73   12.443%   $239.2   $239.20   $239.20   $239.20  
  Purchase #6 $250.32   4.170%   $260.7583   $260.76   $260.75   $260.80  
  Purchase #7 $245.83   11.459%   $273.9997   $274.00   $274.00   $274.00  
  7 purchase totals = $1,322.30       $1,417.1995   $1,417.21   $1,417.20   $1,417.20