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 $24.69   6.459%   $26.2847   $26.28   $26.30   $26.30  
  Purchase #2 $206.93   13.400%   $234.6586   $234.66   $234.65   $234.70  
  Purchase #3 $172.67   7.174%   $185.0573   $185.06   $185.05   $185.10  
  Purchase #4 $189.35   13.312%   $214.5563   $214.56   $214.55   $214.60  
  Purchase #5 $233.72   5.790%   $247.2524   $247.25   $247.25   $247.30  
  Purchase #6 $72.25   5.184%   $75.9954   $76.00   $76.00   $76.00  
  Purchase #7 $59.46   6.663%   $63.4218   $63.42   $63.40   $63.40  
  7 purchase totals = $959.07       $1,047.2265   $1,047.23   $1,047.20   $1,047.40