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 $112.87   5.775%   $119.3882   $119.39   $119.40   $119.40  
  Purchase #2 $52.41   4.309%   $54.6683   $54.67   $54.65   $54.70  
  Purchase #3 $242.51   6.108%   $257.3225   $257.32   $257.30   $257.30  
  Purchase #4 $49.77   4.305%   $51.9126   $51.91   $51.90   $51.90  
  Purchase #5 $174.45   11.774%   $194.9897   $194.99   $195.00   $195.00  
  Purchase #6 $181.88   13.528%   $206.4847   $206.48   $206.50   $206.50  
  Purchase #7 $11.67   4.756%   $12.225   $12.23   $12.25   $12.20  
  7 purchase totals = $825.56       $896.9910   $896.99   $897.00   $897.00