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 $94.88   10.274%   $104.628   $104.63   $104.65   $104.60  
  Purchase #2 $42.60   11.382%   $47.4487   $47.45   $47.45   $47.40  
  Purchase #3 $238.90   13.826%   $271.9303   $271.93   $271.95   $271.90  
  Purchase #4 $210.81   7.546%   $226.7177   $226.72   $226.70   $226.70  
  Purchase #5 $228.52   13.622%   $259.649   $259.65   $259.65   $259.60  
  Purchase #6 $48.53   13.810%   $55.232   $55.23   $55.25   $55.20  
  Purchase #7 $215.26   11.630%   $240.2947   $240.29   $240.30   $240.30  
  7 purchase totals = $1,079.50       $1,205.9004   $1,205.90   $1,205.95   $1,205.70