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 $241.73   12.770%   $272.5989   $272.60   $272.60   $272.60  
  Purchase #2 $70.52   10.190%   $77.706   $77.71   $77.70   $77.70  
  Purchase #3 $104.55   5.855%   $110.6714   $110.67   $110.65   $110.70  
  Purchase #4 $42.66   4.589%   $44.6177   $44.62   $44.60   $44.60  
  Purchase #5 $162.91   5.155%   $171.308   $171.31   $171.30   $171.30  
  Purchase #6 $238.38   8.428%   $258.4707   $258.47   $258.45   $258.50  
  Purchase #7 $98.99   13.131%   $111.9884   $111.99   $112.00   $112.00  
  7 purchase totals = $959.74       $1,047.3611   $1,047.37   $1,047.30   $1,047.40