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 $239.93   10.714%   $265.6361   $265.64   $265.65   $265.60  
  Purchase #2 $183.44   4.339%   $191.3995   $191.40   $191.40   $191.40  
  Purchase #3 $152.37   5.630%   $160.9484   $160.95   $160.95   $160.90  
  Purchase #4 $137.40   13.232%   $155.5808   $155.58   $155.60   $155.60  
  Purchase #5 $203.60   13.728%   $231.5502   $231.55   $231.55   $231.60  
  Purchase #6 $236.43   5.810%   $250.1666   $250.17   $250.15   $250.20  
  Purchase #7 $107.54   13.646%   $122.2149   $122.21   $122.20   $122.20  
  7 purchase totals = $1,260.71       $1,377.4965   $1,377.50   $1,377.50   $1,377.50