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 $224.36   13.554%   $254.7698   $254.77   $254.75   $254.80  
  Purchase #2 $250.66   5.254%   $263.8297   $263.83   $263.85   $263.80  
  Purchase #3 $45.59   3.637%   $47.2481   $47.25   $47.25   $47.20  
  Purchase #4 $6.69   8.344%   $7.2482   $7.25   $7.25   $7.20  
  Purchase #5 $100.75   3.871%   $104.65   $104.65   $104.65   $104.70  
  Purchase #6 $163.93   8.527%   $177.9083   $177.91   $177.90   $177.90  
  Purchase #7 $207.58   5.829%   $219.6798   $219.68   $219.70   $219.70  
  7 purchase totals = $999.56       $1,075.3339   $1,075.34   $1,075.35   $1,075.30