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 $24.55   9.142%   $26.7944   $26.79   $26.80   $26.80  
  Purchase #2 $208.83   9.714%   $229.1157   $229.12   $229.10   $229.10  
  Purchase #3 $67.85   5.663%   $71.6923   $71.69   $71.70   $71.70  
  Purchase #4 $233.89   3.467%   $241.999   $242.00   $242.00   $242.00  
  Purchase #5 $59.77   10.874%   $66.2694   $66.27   $66.25   $66.30  
  Purchase #6 $30.54   13.153%   $34.5569   $34.56   $34.55   $34.60  
  Purchase #7 $78.51   8.435%   $85.1323   $85.13   $85.15   $85.10  
  7 purchase totals = $703.94       $755.5600   $755.56   $755.55   $755.60