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 $183.71   11.447%   $204.7393   $204.74   $204.75   $204.70  
  Purchase #2 $25.82   6.165%   $27.4118   $27.41   $27.40   $27.40  
  Purchase #3 $50.81   3.873%   $52.7779   $52.78   $52.80   $52.80  
  Purchase #4 $193.69   9.360%   $211.8194   $211.82   $211.80   $211.80  
  Purchase #5 $186.81   11.151%   $207.6412   $207.64   $207.65   $207.60  
  Purchase #6 $98.44   8.159%   $106.4717   $106.47   $106.45   $106.50  
  Purchase #7 $241.75   8.211%   $261.6001   $261.60   $261.60   $261.60  
  7 purchase totals = $981.03       $1,072.4614   $1,072.46   $1,072.45   $1,072.40