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 $190.69   11.157%   $211.9653   $211.97   $211.95   $212.00  
  Purchase #2 $20.97   8.149%   $22.6788   $22.68   $22.70   $22.70  
  Purchase #3 $250.75   8.570%   $272.2393   $272.24   $272.25   $272.20  
  Purchase #4 $33.50   9.758%   $36.7689   $36.77   $36.75   $36.80  
  Purchase #5 $100.34   4.326%   $104.6807   $104.68   $104.70   $104.70  
  Purchase #6 $128.56   13.604%   $146.0493   $146.05   $146.05   $146.00  
  Purchase #7 $240.36   8.871%   $261.6823   $261.68   $261.70   $261.70  
  7 purchase totals = $965.17       $1,056.0646   $1,056.07   $1,056.10   $1,056.10