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 $217.45   11.180%   $241.7609   $241.76   $241.75   $241.80  
  Purchase #2 $213.62   12.674%   $240.6942   $240.69   $240.70   $240.70  
  Purchase #3 $69.28   6.354%   $73.6821   $73.68   $73.70   $73.70  
  Purchase #4 $234.61   8.652%   $254.9085   $254.91   $254.90   $254.90  
  Purchase #5 $130.51   7.462%   $140.2487   $140.25   $140.25   $140.20  
  Purchase #6 $34.26   12.423%   $38.5161   $38.52   $38.50   $38.50  
  Purchase #7 $34.54   7.281%   $37.0549   $37.05   $37.05   $37.10  
  7 purchase totals = $934.27       $1,026.8654   $1,026.86   $1,026.85   $1,026.90