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 $53.70   13.816%   $61.1192   $61.12   $61.10   $61.10  
  Purchase #2 $176.38   13.629%   $200.4188   $200.42   $200.40   $200.40  
  Purchase #3 $231.93   9.797%   $254.6522   $254.65   $254.65   $254.70  
  Purchase #4 $66.31   4.105%   $69.032   $69.03   $69.05   $69.00  
  Purchase #5 $71.87   4.164%   $74.8627   $74.86   $74.85   $74.90  
  Purchase #6 $42.52   5.542%   $44.8765   $44.88   $44.90   $44.90  
  Purchase #7 $233.53   13.268%   $264.5148   $264.51   $264.50   $264.50  
  7 purchase totals = $876.24       $969.4762   $969.47   $969.45   $969.50