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 $68.92   12.819%   $77.7549   $77.75   $77.75   $77.80  
  Purchase #2 $243.64   6.617%   $259.7617   $259.76   $259.75   $259.80  
  Purchase #3 $130.38   4.812%   $136.6539   $136.65   $136.65   $136.70  
  Purchase #4 $70.78   12.719%   $79.7825   $79.78   $79.80   $79.80  
  Purchase #5 $41.43   8.197%   $44.826   $44.83   $44.85   $44.80  
  Purchase #6 $231.66   4.814%   $242.8121   $242.81   $242.80   $242.80  
  Purchase #7 $40.91   7.651%   $44.04   $44.04   $44.05   $44.00  
  7 purchase totals = $827.72       $885.6311   $885.62   $885.65   $885.70