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 $180.85   8.216%   $195.7086   $195.71   $195.70   $195.70  
  Purchase #2 $137.31   11.789%   $153.4975   $153.50   $153.50   $153.50  
  Purchase #3 $41.60   5.135%   $43.7362   $43.74   $43.75   $43.70  
  Purchase #4 $124.92   11.493%   $139.2771   $139.28   $139.30   $139.30  
  Purchase #5 $237.74   3.177%   $245.293   $245.29   $245.30   $245.30  
  Purchase #6 $67.90   9.119%   $74.0918   $74.09   $74.10   $74.10  
  Purchase #7 $52.25   11.827%   $58.4296   $58.43   $58.45   $58.40  
  7 purchase totals = $842.57       $910.0338   $910.04   $910.10   $910.00