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 $64.97   12.660%   $73.1952   $73.20   $73.20   $73.20  
  Purchase #2 $113.55   3.175%   $117.1552   $117.16   $117.15   $117.20  
  Purchase #3 $147.25   6.423%   $156.7079   $156.71   $156.70   $156.70  
  Purchase #4 $54.72   10.144%   $60.2708   $60.27   $60.25   $60.30  
  Purchase #5 $126.63   3.404%   $130.9405   $130.94   $130.95   $130.90  
  Purchase #6 $11.88   6.463%   $12.6478   $12.65   $12.65   $12.60  
  Purchase #7 $207.77   7.298%   $222.9331   $222.93   $222.95   $222.90  
  7 purchase totals = $726.77       $773.8505   $773.86   $773.85   $773.80