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 $246.25   12.182%   $276.2482   $276.25   $276.25   $276.20  
  Purchase #2 $250.96   13.416%   $284.6288   $284.63   $284.65   $284.60  
  Purchase #3 $200.75   11.622%   $224.0812   $224.08   $224.10   $224.10  
  Purchase #4 $171.92   8.460%   $186.4644   $186.46   $186.45   $186.50  
  Purchase #5 $54.71   6.137%   $58.0676   $58.07   $58.05   $58.10  
  Purchase #6 $40.40   9.567%   $44.2651   $44.27   $44.25   $44.30  
  Purchase #7 $208.30   11.288%   $231.8129   $231.81   $231.80   $231.80  
  7 purchase totals = $1,173.29       $1,305.5682   $1,305.57   $1,305.55   $1,305.60