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 $66.38   11.422%   $73.9619   $73.96   $73.95   $74.00  
  Purchase #2 $163.40   8.659%   $177.5488   $177.55   $177.55   $177.50  
  Purchase #3 $93.65   11.427%   $104.3514   $104.35   $104.35   $104.40  
  Purchase #4 $206.67   8.696%   $224.642   $224.64   $224.65   $224.60  
  Purchase #5 $168.64   5.514%   $177.9388   $177.94   $177.95   $177.90  
  Purchase #6 $24.95   13.783%   $28.3889   $28.39   $28.40   $28.40  
  Purchase #7 $47.68   13.737%   $54.2298   $54.23   $54.25   $54.20  
  7 purchase totals = $771.37       $841.0616   $841.06   $841.10   $841.00