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 $68.85   13.622%   $78.2287   $78.23   $78.25   $78.20  
  Purchase #2 $11.69   13.640%   $13.2845   $13.28   $13.30   $13.30  
  Purchase #3 $210.26   13.704%   $239.074   $239.07   $239.05   $239.10  
  Purchase #4 $143.55   5.629%   $151.6304   $151.63   $151.65   $151.60  
  Purchase #5 $127.27   3.172%   $131.307   $131.31   $131.30   $131.30  
  Purchase #6 $91.62   3.799%   $95.1006   $95.10   $95.10   $95.10  
  Purchase #7 $235.49   13.821%   $268.0371   $268.04   $268.05   $268.00  
  7 purchase totals = $888.73       $976.6623   $976.66   $976.70   $976.60