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 $48.56   11.819%   $54.2993   $54.30   $54.30   $54.30  
  Purchase #2 $174.70   13.706%   $198.6444   $198.64   $198.65   $198.60  
  Purchase #3 $98.68   6.134%   $104.733   $104.73   $104.75   $104.70  
  Purchase #4 $47.56   10.499%   $52.5533   $52.55   $52.55   $52.60  
  Purchase #5 $173.64   11.613%   $193.8048   $193.80   $193.80   $193.80  
  Purchase #6 $84.77   5.819%   $89.7028   $89.70   $89.70   $89.70  
  Purchase #7 $208.36   8.524%   $226.1206   $226.12   $226.10   $226.10  
  7 purchase totals = $836.27       $919.8582   $919.84   $919.85   $919.80