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 $22.44   4.738%   $23.5032   $23.50   $23.50   $23.50  
  Purchase #2 $111.87   6.777%   $119.4514   $119.45   $119.45   $119.50  
  Purchase #3 $105.86   12.607%   $119.2058   $119.21   $119.20   $119.20  
  Purchase #4 $157.67   3.523%   $163.2247   $163.22   $163.20   $163.20  
  Purchase #5 $80.42   8.289%   $87.086   $87.09   $87.10   $87.10  
  Purchase #6 $32.74   7.647%   $35.2436   $35.24   $35.25   $35.20  
  Purchase #7 $194.95   7.109%   $208.809   $208.81   $208.80   $208.80  
  7 purchase totals = $705.95       $756.5237   $756.52   $756.50   $756.50