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 $245.26   5.170%   $257.9399   $257.94   $257.95   $257.90  
  Purchase #2 $59.99   10.490%   $66.283   $66.28   $66.30   $66.30  
  Purchase #3 $208.32   12.559%   $234.4829   $234.48   $234.50   $234.50  
  Purchase #4 $162.66   7.607%   $175.0335   $175.03   $175.05   $175.00  
  Purchase #5 $220.28   13.555%   $250.139   $250.14   $250.15   $250.10  
  Purchase #6 $119.40   11.868%   $133.5704   $133.57   $133.55   $133.60  
  Purchase #7 $157.78   13.439%   $178.9841   $178.98   $179.00   $179.00  
  7 purchase totals = $1,173.69       $1,296.4328   $1,296.42   $1,296.50   $1,296.40