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 $53.82   13.390%   $61.0265   $61.03   $61.05   $61.00  
  Purchase #2 $238.66   9.429%   $261.1633   $261.16   $261.15   $261.20  
  Purchase #3 $33.59   3.590%   $34.7959   $34.80   $34.80   $34.80  
  Purchase #4 $237.62   5.191%   $249.9549   $249.95   $249.95   $250.00  
  Purchase #5 $100.31   8.251%   $108.5866   $108.59   $108.60   $108.60  
  Purchase #6 $201.26   3.819%   $208.9461   $208.95   $208.95   $208.90  
  Purchase #7 $248.53   10.513%   $274.658   $274.66   $274.65   $274.70  
  7 purchase totals = $1,113.79       $1,199.1313   $1,199.14   $1,199.15   $1,199.20