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 $176.44   12.473%   $198.4474   $198.45   $198.45   $198.40  
  Purchase #2 $248.74   3.327%   $257.0156   $257.02   $257.00   $257.00  
  Purchase #3 $192.43   12.222%   $215.9488   $215.95   $215.95   $215.90  
  Purchase #4 $216.31   11.843%   $241.9276   $241.93   $241.95   $241.90  
  Purchase #5 $70.61   6.213%   $74.997   $75.00   $75.00   $75.00  
  Purchase #6 $208.93   11.164%   $232.2549   $232.25   $232.25   $232.30  
  Purchase #7 $111.77   5.683%   $118.1219   $118.12   $118.10   $118.10  
  7 purchase totals = $1,225.23       $1,338.7132   $1,338.72   $1,338.70   $1,338.60