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 $246.50   10.760%   $273.0234   $273.02   $273.00   $273.00  
  Purchase #2 $23.39   6.483%   $24.9064   $24.91   $24.90   $24.90  
  Purchase #3 $236.66   9.581%   $259.3344   $259.33   $259.35   $259.30  
  Purchase #4 $105.55   10.584%   $116.7214   $116.72   $116.70   $116.70  
  Purchase #5 $29.81   3.462%   $30.842   $30.84   $30.85   $30.80  
  Purchase #6 $59.76   3.217%   $61.6825   $61.68   $61.70   $61.70  
  Purchase #7 $125.54   11.325%   $139.7574   $139.76   $139.75   $139.80  
  7 purchase totals = $827.21       $906.2675   $906.26   $906.25   $906.20