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 $5.86   3.513%   $6.0659   $6.07   $6.05   $6.10  
  Purchase #2 $52.66   7.763%   $56.748   $56.75   $56.75   $56.70  
  Purchase #3 $200.43   7.615%   $215.6927   $215.69   $215.70   $215.70  
  Purchase #4 $176.28   11.834%   $197.141   $197.14   $197.15   $197.10  
  Purchase #5 $182.56   11.277%   $203.1473   $203.15   $203.15   $203.10  
  Purchase #6 $196.59   12.225%   $220.6231   $220.62   $220.60   $220.60  
  Purchase #7 $137.89   13.425%   $156.4017   $156.40   $156.40   $156.40  
  7 purchase totals = $952.27       $1,055.8197   $1,055.82   $1,055.80   $1,055.70