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 $250.79   8.284%   $271.5654   $271.57   $271.55   $271.60  
  Purchase #2 $137.95   13.569%   $156.6684   $156.67   $156.65   $156.70  
  Purchase #3 $210.60   7.729%   $226.8773   $226.88   $226.90   $226.90  
  Purchase #4 $130.81   11.789%   $146.2312   $146.23   $146.25   $146.20  
  Purchase #5 $42.98   13.162%   $48.637   $48.64   $48.65   $48.60  
  Purchase #6 $183.51   3.624%   $190.1604   $190.16   $190.15   $190.20  
  Purchase #7 $50.41   9.236%   $55.0659   $55.07   $55.05   $55.10  
  7 purchase totals = $1,007.05       $1,095.2056   $1,095.22   $1,095.20   $1,095.30