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 $250.37   4.136%   $260.7253   $260.73   $260.75   $260.70  
  Purchase #2 $228.77   4.541%   $239.1584   $239.16   $239.15   $239.20  
  Purchase #3 $11.35   10.683%   $12.5625   $12.56   $12.55   $12.60  
  Purchase #4 $226.54   9.151%   $247.2707   $247.27   $247.25   $247.30  
  Purchase #5 $82.32   13.146%   $93.1418   $93.14   $93.15   $93.10  
  Purchase #6 $44.87   3.233%   $46.3206   $46.32   $46.30   $46.30  
  Purchase #7 $87.49   10.173%   $96.3904   $96.39   $96.40   $96.40  
  7 purchase totals = $931.71       $995.5697   $995.57   $995.55   $995.60