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 $245.88   10.712%   $272.2187   $272.22   $272.20   $272.20  
  Purchase #2 $212.69   5.156%   $223.6563   $223.66   $223.65   $223.70  
  Purchase #3 $72.61   5.746%   $76.7822   $76.78   $76.80   $76.80  
  Purchase #4 $19.47   4.126%   $20.2733   $20.27   $20.25   $20.30  
  Purchase #5 $246.51   5.231%   $259.4049   $259.40   $259.40   $259.40  
  Purchase #6 $115.86   3.372%   $119.7668   $119.77   $119.75   $119.80  
  Purchase #7 $96.45   6.235%   $102.4637   $102.46   $102.45   $102.50  
  7 purchase totals = $1,009.47       $1,074.5659   $1,074.56   $1,074.50   $1,074.70