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 $191.92   5.478%   $202.4334   $202.43   $202.45   $202.40  
  Purchase #2 $250.33   10.656%   $277.0052   $277.01   $277.00   $277.00  
  Purchase #3 $87.34   6.188%   $92.7446   $92.74   $92.75   $92.70  
  Purchase #4 $19.81   8.748%   $21.543   $21.54   $21.55   $21.50  
  Purchase #5 $242.57   3.173%   $250.2667   $250.27   $250.25   $250.30  
  Purchase #6 $118.91   6.822%   $127.022   $127.02   $127.00   $127.00  
  Purchase #7 $93.35   12.114%   $104.6584   $104.66   $104.65   $104.70  
  7 purchase totals = $1,004.23       $1,075.6733   $1,075.67   $1,075.65   $1,075.60