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 $84.25   10.110%   $92.7677   $92.77   $92.75   $92.80  
  Purchase #2 $220.91   12.469%   $248.4553   $248.46   $248.45   $248.50  
  Purchase #3 $163.44   11.391%   $182.0575   $182.06   $182.05   $182.10  
  Purchase #4 $135.71   5.405%   $143.0451   $143.05   $143.05   $143.00  
  Purchase #5 $121.62   6.584%   $129.6275   $129.63   $129.65   $129.60  
  Purchase #6 $133.48   9.680%   $146.4009   $146.40   $146.40   $146.40  
  Purchase #7 $136.80   11.253%   $152.1941   $152.19   $152.20   $152.20  
  7 purchase totals = $996.21       $1,094.5481   $1,094.56   $1,094.55   $1,094.60