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 $24.56   5.798%   $25.984   $25.98   $26.00   $26.00  
  Purchase #2 $9.93   3.322%   $10.2599   $10.26   $10.25   $10.30  
  Purchase #3 $192.77   3.173%   $198.8866   $198.89   $198.90   $198.90  
  Purchase #4 $81.66   3.831%   $84.7884   $84.79   $84.80   $84.80  
  Purchase #5 $200.36   5.379%   $211.1374   $211.14   $211.15   $211.10  
  Purchase #6 $208.69   3.604%   $216.2112   $216.21   $216.20   $216.20  
  Purchase #7 $151.49   6.591%   $161.4747   $161.47   $161.45   $161.50  
  7 purchase totals = $869.46       $908.7422   $908.74   $908.75   $908.80