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 $35.47   3.209%   $36.6082   $36.61   $36.60   $36.60  
  Purchase #2 $134.55   5.219%   $141.5722   $141.57   $141.55   $141.60  
  Purchase #3 $120.51   11.318%   $134.1493   $134.15   $134.15   $134.10  
  Purchase #4 $97.91   9.785%   $107.4905   $107.49   $107.50   $107.50  
  Purchase #5 $24.62   6.676%   $26.2636   $26.26   $26.25   $26.30  
  Purchase #6 $186.50   13.281%   $211.2691   $211.27   $211.25   $211.30  
  Purchase #7 $152.90   10.298%   $168.6456   $168.65   $168.65   $168.60  
  7 purchase totals = $752.46       $825.9985   $826.00   $825.95   $826.00