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 $247.42   10.756%   $274.0325   $274.03   $274.05   $274.00  
  Purchase #2 $111.42   4.321%   $116.2345   $116.23   $116.25   $116.20  
  Purchase #3 $85.54   9.455%   $93.6278   $93.63   $93.65   $93.60  
  Purchase #4 $55.83   6.460%   $59.4366   $59.44   $59.45   $59.40  
  Purchase #5 $175.41   4.197%   $182.772   $182.77   $182.75   $182.80  
  Purchase #6 $11.69   8.859%   $12.7256   $12.73   $12.75   $12.70  
  Purchase #7 $127.28   7.173%   $136.4098   $136.41   $136.40   $136.40  
  7 purchase totals = $814.59       $875.2388   $875.24   $875.30   $875.10