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 $149.26   8.507%   $161.9575   $161.96   $161.95   $162.00  
  Purchase #2 $231.87   12.151%   $260.0445   $260.04   $260.05   $260.00  
  Purchase #3 $113.41   9.149%   $123.7859   $123.79   $123.80   $123.80  
  Purchase #4 $208.89   13.568%   $237.2322   $237.23   $237.25   $237.20  
  Purchase #5 $249.56   3.387%   $258.0126   $258.01   $258.00   $258.00  
  Purchase #6 $243.66   12.203%   $273.3938   $273.39   $273.40   $273.40  
  Purchase #7 $71.37   11.266%   $79.4105   $79.41   $79.40   $79.40  
  7 purchase totals = $1,268.02       $1,393.8370   $1,393.83   $1,393.85   $1,393.80