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 $58.74   13.169%   $66.4755   $66.48   $66.50   $66.50  
  Purchase #2 $22.77   13.419%   $25.8255   $25.83   $25.85   $25.80  
  Purchase #3 $190.44   4.233%   $198.5013   $198.50   $198.50   $198.50  
  Purchase #4 $71.96   4.457%   $75.1673   $75.17   $75.15   $75.20  
  Purchase #5 $235.70   11.258%   $262.2351   $262.24   $262.25   $262.20  
  Purchase #6 $201.81   11.783%   $225.5893   $225.59   $225.60   $225.60  
  Purchase #7 $34.27   13.224%   $38.8019   $38.80   $38.80   $38.80  
  7 purchase totals = $815.69       $892.5959   $892.61   $892.65   $892.60