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 $23.55   4.484%   $24.606   $24.61   $24.60   $24.60  
  Purchase #2 $122.39   3.774%   $127.009   $127.01   $127.00   $127.00  
  Purchase #3 $130.35   9.854%   $143.1947   $143.19   $143.20   $143.20  
  Purchase #4 $78.81   7.201%   $84.4851   $84.49   $84.50   $84.50  
  Purchase #5 $69.98   7.651%   $75.3342   $75.33   $75.35   $75.30  
  Purchase #6 $63.37   12.347%   $71.1943   $71.19   $71.20   $71.20  
  Purchase #7 $186.77   6.284%   $198.5066   $198.51   $198.50   $198.50  
  7 purchase totals = $675.22       $724.3299   $724.33   $724.35   $724.30