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 $239.26   8.792%   $260.2957   $260.30   $260.30   $260.30  
  Purchase #2 $213.31   8.425%   $231.2814   $231.28   $231.30   $231.30  
  Purchase #3 $190.57   7.647%   $205.1429   $205.14   $205.15   $205.10  
  Purchase #4 $231.35   7.176%   $247.9517   $247.95   $247.95   $248.00  
  Purchase #5 $231.94   12.198%   $260.232   $260.23   $260.25   $260.20  
  Purchase #6 $193.93   13.792%   $220.6768   $220.68   $220.70   $220.70  
  Purchase #7 $119.72   13.489%   $135.869   $135.87   $135.85   $135.90  
  7 purchase totals = $1,420.08       $1,561.4495   $1,561.45   $1,561.50   $1,561.50