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 $23.59   10.260%   $26.0103   $26.01   $26.00   $26.00  
  Purchase #2 $92.85   11.588%   $103.6095   $103.61   $103.60   $103.60  
  Purchase #3 $143.68   13.804%   $163.5136   $163.51   $163.50   $163.50  
  Purchase #4 $66.37   3.153%   $68.4626   $68.46   $68.45   $68.50  
  Purchase #5 $146.47   6.211%   $155.5673   $155.57   $155.55   $155.60  
  Purchase #6 $69.85   4.407%   $72.9283   $72.93   $72.95   $72.90  
  Purchase #7 $249.29   7.660%   $268.3856   $268.39   $268.40   $268.40  
  7 purchase totals = $792.10       $858.4772   $858.48   $858.45   $858.50