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 $49.51   12.314%   $55.6067   $55.61   $55.60   $55.60  
  Purchase #2 $222.50   4.838%   $233.2646   $233.26   $233.25   $233.30  
  Purchase #3 $29.26   10.206%   $32.2463   $32.25   $32.25   $32.20  
  Purchase #4 $176.36   9.445%   $193.0172   $193.02   $193.00   $193.00  
  Purchase #5 $205.61   3.855%   $213.5363   $213.54   $213.55   $213.50  
  Purchase #6 $117.87   9.194%   $128.707   $128.71   $128.70   $128.70  
  Purchase #7 $242.99   9.803%   $266.8103   $266.81   $266.80   $266.80  
  7 purchase totals = $1,044.10       $1,123.1884   $1,123.20   $1,123.15   $1,123.10