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 $104.93   7.681%   $112.9897   $112.99   $113.00   $113.00  
  Purchase #2 $153.38   11.443%   $170.9313   $170.93   $170.95   $170.90  
  Purchase #3 $46.53   9.671%   $51.0299   $51.03   $51.05   $51.00  
  Purchase #4 $124.43   10.753%   $137.81   $137.81   $137.80   $137.80  
  Purchase #5 $26.92   12.629%   $30.3197   $30.32   $30.30   $30.30  
  Purchase #6 $51.99   6.187%   $55.2066   $55.21   $55.20   $55.20  
  Purchase #7 $192.41   13.253%   $217.9101   $217.91   $217.90   $217.90  
  7 purchase totals = $700.59       $776.1973   $776.20   $776.20   $776.10