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 $237.42   12.492%   $267.0785   $267.08   $267.10   $267.10  
  Purchase #2 $51.75   9.402%   $56.6155   $56.62   $56.60   $56.60  
  Purchase #3 $229.97   12.422%   $258.5369   $258.54   $258.55   $258.50  
  Purchase #4 $183.56   5.807%   $194.2193   $194.22   $194.20   $194.20  
  Purchase #5 $115.34   5.493%   $121.6756   $121.68   $121.70   $121.70  
  Purchase #6 $200.79   11.643%   $224.168   $224.17   $224.15   $224.20  
  Purchase #7 $64.99   11.688%   $72.586   $72.59   $72.60   $72.60  
  7 purchase totals = $1,083.82       $1,194.8798   $1,194.90   $1,194.90   $1,194.90