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 $112.70   11.121%   $125.2334   $125.23   $125.25   $125.20  
  Purchase #2 $236.42   9.564%   $259.0312   $259.03   $259.05   $259.00  
  Purchase #3 $163.44   12.448%   $183.785   $183.79   $183.80   $183.80  
  Purchase #4 $7.44   13.250%   $8.4258   $8.43   $8.45   $8.40  
  Purchase #5 $247.38   10.832%   $274.1762   $274.18   $274.20   $274.20  
  Purchase #6 $39.94   13.822%   $45.4605   $45.46   $45.45   $45.50  
  Purchase #7 $26.64   5.455%   $28.0932   $28.09   $28.10   $28.10  
  7 purchase totals = $833.96       $924.2053   $924.21   $924.30   $924.20