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 $162.64   3.618%   $168.5243   $168.52   $168.50   $168.50  
  Purchase #2 $122.34   8.409%   $132.6276   $132.63   $132.65   $132.60  
  Purchase #3 $122.57   8.619%   $133.1343   $133.13   $133.15   $133.10  
  Purchase #4 $242.71   7.318%   $260.4715   $260.47   $260.45   $260.50  
  Purchase #5 $32.71   5.629%   $34.5512   $34.55   $34.55   $34.60  
  Purchase #6 $72.26   4.833%   $75.7523   $75.75   $75.75   $75.80  
  Purchase #7 $201.70   3.446%   $208.6506   $208.65   $208.65   $208.70  
  7 purchase totals = $956.93       $1,013.7118   $1,013.70   $1,013.70   $1,013.80