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 $42.91   13.720%   $48.7973   $48.80   $48.80   $48.80  
  Purchase #2 $239.89   3.487%   $248.255   $248.26   $248.25   $248.30  
  Purchase #3 $65.53   6.184%   $69.5824   $69.58   $69.60   $69.60  
  Purchase #4 $231.51   13.806%   $263.4723   $263.47   $263.45   $263.50  
  Purchase #5 $48.63   5.314%   $51.2142   $51.21   $51.20   $51.20  
  Purchase #6 $87.59   6.335%   $93.1388   $93.14   $93.15   $93.10  
  Purchase #7 $127.28   13.414%   $144.3533   $144.35   $144.35   $144.40  
  7 purchase totals = $843.34       $918.8133   $918.81   $918.80   $918.90