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 $248.27   6.794%   $265.1375   $265.14   $265.15   $265.10  
  Purchase #2 $48.46   4.656%   $50.7163   $50.72   $50.70   $50.70  
  Purchase #3 $115.89   13.329%   $131.337   $131.34   $131.35   $131.30  
  Purchase #4 $117.65   7.666%   $126.669   $126.67   $126.65   $126.70  
  Purchase #5 $173.88   7.254%   $186.4933   $186.49   $186.50   $186.50  
  Purchase #6 $157.94   12.203%   $177.2134   $177.21   $177.20   $177.20  
  Purchase #7 $238.59   13.387%   $270.53   $270.53   $270.55   $270.50  
  7 purchase totals = $1,100.68       $1,208.0965   $1,208.10   $1,208.10   $1,208.00