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 $179.27   12.787%   $202.1933   $202.19   $202.20   $202.20  
  Purchase #2 $88.45   10.782%   $97.9867   $97.99   $98.00   $98.00  
  Purchase #3 $183.37   3.379%   $189.5661   $189.57   $189.55   $189.60  
  Purchase #4 $174.94   9.543%   $191.6345   $191.63   $191.65   $191.60  
  Purchase #5 $156.39   5.172%   $164.4785   $164.48   $164.50   $164.50  
  Purchase #6 $52.79   8.545%   $57.3009   $57.30   $57.30   $57.30  
  Purchase #7 $41.30   12.617%   $46.5108   $46.51   $46.50   $46.50  
  7 purchase totals = $876.51       $949.6708   $949.67   $949.70   $949.70