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 $92.81   5.689%   $98.09   $98.09   $98.10   $98.10  
  Purchase #2 $232.50   9.688%   $255.0246   $255.02   $255.00   $255.00  
  Purchase #3 $104.95   7.132%   $112.435   $112.44   $112.45   $112.40  
  Purchase #4 $147.60   3.507%   $152.7763   $152.78   $152.80   $152.80  
  Purchase #5 $242.74   7.804%   $261.6834   $261.68   $261.70   $261.70  
  Purchase #6 $238.75   3.633%   $247.4238   $247.42   $247.40   $247.40  
  Purchase #7 $63.68   11.202%   $70.8134   $70.81   $70.80   $70.80  
  7 purchase totals = $1,123.03       $1,198.2465   $1,198.24   $1,198.25   $1,198.20