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 $227.52   8.124%   $246.0037   $246.00   $246.00   $246.00  
  Purchase #2 $247.47   10.338%   $273.0534   $273.05   $273.05   $273.10  
  Purchase #3 $19.60   13.618%   $22.2691   $22.27   $22.25   $22.30  
  Purchase #4 $102.78   13.417%   $116.57   $116.57   $116.55   $116.60  
  Purchase #5 $42.80   8.495%   $46.4359   $46.44   $46.45   $46.40  
  Purchase #6 $250.99   5.456%   $264.684   $264.68   $264.70   $264.70  
  Purchase #7 $20.40   10.816%   $22.6065   $22.61   $22.60   $22.60  
  7 purchase totals = $911.56       $991.6226   $991.62   $991.60   $991.70