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 $124.36   13.852%   $141.5863   $141.59   $141.60   $141.60  
  Purchase #2 $131.48   3.643%   $136.2698   $136.27   $136.25   $136.30  
  Purchase #3 $225.47   8.262%   $244.0983   $244.10   $244.10   $244.10  
  Purchase #4 $85.65   7.613%   $92.1705   $92.17   $92.15   $92.20  
  Purchase #5 $166.89   5.274%   $175.6918   $175.69   $175.70   $175.70  
  Purchase #6 $115.80   8.808%   $125.9997   $126.00   $126.00   $126.00  
  Purchase #7 $143.70   12.382%   $161.4929   $161.49   $161.50   $161.50  
  7 purchase totals = $993.35       $1,077.3093   $1,077.31   $1,077.30   $1,077.40